Incorporate the 3.34.1 patches into the reuse-schema branch.

FossilOrigin-Name: cc0e582854be11c29186d535130344c5486deb124ec4135a50ee1de21ea44a1d
Version 3.34.1
2021-01-20 15:10:48 +00:00 · 2021-01-20 14:10:07 +00:00 · 2021-01-19 20:38:13 +00:00 · 2021-01-19 20:17:46 +00:00 · 2021-01-19 20:09:44 +00:00 · 2021-01-19 20:04:37 +00:00
53 changed files with 3354 additions and 256 deletions
@@ -418,6 +418,7 @@ TESTSRC = \
  $(TOP)/src/test_quota.c \
  $(TOP)/src/test_rtree.c \
  $(TOP)/src/test_schema.c \
+  $(TOP)/src/test_schemapool.c \
  $(TOP)/src/test_server.c \
  $(TOP)/src/test_superlock.c \
  $(TOP)/src/test_syscall.c \
@@ -476,6 +477,7 @@ TESTSRC2 = \
  $(TOP)/src/bitvec.c \
  $(TOP)/src/btree.c \
  $(TOP)/src/build.c \
+  $(TOP)/src/callback.c \
  $(TOP)/src/ctime.c \
  $(TOP)/src/date.c \
  $(TOP)/src/dbpage.c \
@@ -1535,6 +1535,7 @@ TESTSRC = \
  $(TOP)\src\test_quota.c \
  $(TOP)\src\test_rtree.c \
  $(TOP)\src\test_schema.c \
+  $(TOP)\src\test_schemapool.c \
  $(TOP)\src\test_server.c \
  $(TOP)\src\test_superlock.c \
  $(TOP)\src\test_syscall.c \
@@ -1 +1 @@
-3.35.0
+3.34.1
@@ -0,0 +1,142 @@
+
+Shared-Schema Mode Notes
+========================
+
+The [reuse-schema](/timeline?r=reuse-schema) branch contains changes 
+to allow SQLite connections to share schemas
+between database connections within the same process in order to save memory.
+Schemas may be shared between multiple databases attached to the same or
+distinct connection handles.
+
+Compile with -DSQLITE\_ENABLE\_SHARED\_SCHEMA in order to enable the
+shared-schema enhancement.  Enabling the shared-schema enhancement causes
+approximately a 0.1% increase in CPU cycles consumed and about a 3000-byte
+increase in the size of the library, even if shared-schema is never used.
+
+Assuming the compile-time requirements are satisfied, the shared-schema
+feature is engaged by opening the database connection using the
+sqlite3&#95;open&#95;v2() API with the SQLITE&#95;OPEN&#95;SHARED&#95;SCHEMA
+flag specified.  The main database and any attached databases will then share
+an in-memory Schema object with any other database opened within the process
+for which: 
+
+  * the contents of the sqlite&#95;master table, including all object names,
+    SQL statements and root pages are identical, and
+  * have the same values for the schema-cookie.
+
+Temp databases (those populated with "CREATE TEMP TABLE" and similar
+statements) never share schemas.
+
+Connections opened with the SQLITE&#95;OPEN&#95;SHARED&#95;SCHEMA flag
+specified may not modify any database schema except that belonging to the
+temp database in anyway. This includes creating or dropping database 
+objects, vacuuming the database, or running ANALYZE when the
+sqlite&#95;stat\[14\] tables do not exist.
+
+For SQLITE&#95;OPEN&#95;SHARED&#95;SCHEMA connections, the
+SQLITE&#95;DBSTATUS&#95;SCHEMA&#95;USED sqlite3&#95;db&#95;status() verb
+distributes the memory used for a shared schema object evenly between all
+database connections that share it.
+
+## The ".shared-schema" Command
+
+The shell tool on this branch contains a special dot-command to help with
+managing databases. The ".shared-schema" dot-command can be used to test
+whether or not two databases are similar enough to share in-memory schemas,
+and to fix minor problems that prevent them from doing so. To test if
+two or more database are compatible, one database is opened directly using 
+the shell tool and the following command issued:
+
+        .shared-schema check <database-1> [<database-2>]...
+
+where &lt;database-1&gt; etc. are replaced with the names of database files
+on disk. For each database specified on the command line, a single line of
+output is produced. If the database can share an in-memory schema with the
+main database opened by the shell tool, the output is of the form:
+
+        <database> is compatible
+
+Otherwise, if the database cannot share a schema with the main db, the output
+is of the form:
+
+        <database> is NOT compatible (<reason>)
+
+where &lt;reason&gt; indicates the cause of the incompatibility. &lt;reason&gt;
+is always one of the following.
+
+<ul>
+  <li> <b>objects</b> - the databases contain a different set schema objects
+  (tables, indexes, views and triggers).
+
+  <li> <b>SQL</b> - the databases contain the same set of objects, but the SQL
+  statements used to create them were not the same.
+
+  <li> <b>root pages</b> - the databases contain the same set of objects created
+  by the same SQL statements, but the root pages are not the same.
+
+  <li> <b>order of sqlite&#95;master rows</b> - the databases contain the same
+  set of objects created by the same SQL statements with the same root pages,
+  but the order of the rows in the sqlite&#95;master tables are different.
+
+  <li> <b>schema cookie</b> - the database schemas are compatible, but the 
+  schema cookie values ("PRAGMA schema&#95;version") are different.
+</ul>
+
+The final three problems in the list above can be fixed using the
+.shared-schema command. To modify such a database so that it can share a 
+schema with the main database, the following shell command is used:
+
+        .shared-schema fix <database-1> [<database-2>]...
+
+If a database can be modified so that it may share a schema with the main
+database opened by the shell tool, output is as follows:
+
+        Fixing <database>... <database> is compatible
+
+If a database does not require modification, or cannot be modified such that
+it can share a schema with the main database, the output of "fix" is identical
+to that of the "check" command.
+
+## Implementation Notes
+
+A single Schema object is never used by more than one database simultaneously,
+regardless of whether or not those databases are attached to the same or
+different database handles. Instead, a pool of schema objects is maintained 
+for each unique sqlite&#95;master-contents/schema-cookie combination
+opened within the process. Each time database schemas are required by a
+connection, for example as part of an sqlite3&#95;prepare\*(),
+sqlite3&#95;blob&#95;open() or sqlite3&#95;blob&#95;open() call, it obtains
+the minimum number of schemas required from the various schema-pools, returning
+them at the end of the call. This means that a single schema-pool only ever
+contains more than one copy of the schema if:
+
+  * Two threads require schemas from the same pool at the same time, or
+  * A single sqlite3&#95;prepare\*() call requires schemas for two or more
+    attached databases that use the same schema-pool.
+
+The size of a schema-pool never shrinks. Each schema pool always maintains 
+a number of schema objects equal to the highwater mark of schema objects
+simultaneously required by clients.
+
+This approach is preferred to allowing multiple databases to use the same
+Schema object simultaneously for three reasons:
+
+  * The Schema object is not completely read-only. For example, the 
+    Index.zIdxAff string is allocated lazily.
+  * Throughout the statement compiler, SQLite uses variables like 
+    Table.pSchema and Index.pSchema with the sqlite3SchemaToIndex() routine
+    in order to determine which attached database a Table or Index object
+    resides in. This mechanism does not work if the same Schema may be
+    used by two or more attached databases.
+  * It may be easier to modify this approach in order to allow
+    SQLITE&#95;OPEN&#95;SHARED&#95;SCHEMA connections to modify database
+    schemas, should that be required.
+
+SQLITE&#95;OPEN&#95;SHARED&#95;SCHEMA connections do not store their
+virtual-table handles in the Table.pVTable list of each table. This would not
+work, as (a) there is no guarantee that a connection will be assigned the same
+Schema object each time it requests one from a schema-pool and (b) a single
+Schema (and therefore Table) object may correspond to tables in two or more
+databases attached to a single connection. Instead, all virtual-table handles
+associated with a single database are stored in a linked-list headed at
+Db.pVTable.
@@ -621,9 +621,11 @@ static void sha3QueryFunc(
    }
    nCol = sqlite3_column_count(pStmt);
    z = sqlite3_sql(pStmt);
-    n = (int)strlen(z);
-    hash_step_vformat(&cx,"S%d:",n);
-    SHA3Update(&cx,(unsigned char*)z,n);
+    if( z ){
+      n = (int)strlen(z);
+      hash_step_vformat(&cx,"S%d:",n);
+      SHA3Update(&cx,(unsigned char*)z,n);
+    }

    /* Compute a hash over the result of the query */
    while( SQLITE_ROW==sqlite3_step(pStmt) ){
@@ -343,6 +343,7 @@ TESTSRC = \
  $(TOP)/src/test_quota.c \
  $(TOP)/src/test_rtree.c \
  $(TOP)/src/test_schema.c \
+  $(TOP)/src/test_schemapool.c \
  $(TOP)/src/test_server.c \
  $(TOP)/src/test_sqllog.c \
  $(TOP)/src/test_superlock.c \
@@ -396,6 +397,7 @@ TESTSRC2 = \
  $(TOP)/src/backup.c \
  $(TOP)/src/btree.c \
  $(TOP)/src/build.c \
+  $(TOP)/src/callback.c \
  $(TOP)/src/date.c \
  $(TOP)/src/dbpage.c \
  $(TOP)/src/dbstat.c \
@@ -1,13 +1,13 @@
-C Fix\sharmless\scompiler\swarnings\sassociated\swith\sthe\srecent\sFTS5\senhancements.
-D 2020-12-04T17:05:16.189
+C Incorporate\sthe\s3.34.1\spatches\sinto\sthe\sreuse-schema\sbranch.
+D 2021-01-20T15:10:48.635
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+F VERSION 9633e2edacc7963299a285b89cbeb832f73316c9ccc58f9a70701a5e8b16513c
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 F doc/pager-invariants.txt 27fed9a70ddad2088750c4a2b493b63853da2710
+F doc/shared_schema.md 759fc374709fccf4e5d2d0cbd05f8fedd38fb022bdd8a6c5b5f492684c7023b9
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 F doc/vfs-shm.txt e101f27ea02a8387ce46a05be2b1a902a021d37a
@@ -321,7 +322,7 @@ F ext/misc/rot13.c 51ac5f51e9d5fd811db58a9c23c628ad5f333c173f1fc53c8491a3603d385
 F ext/misc/scrub.c 2a44b0d44c69584c0580ad2553f6290a307a49df4668941d2812135bfb96a946
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 F ext/misc/sha1.c c8f2253c8792ffab9517695ea7d88c079f0395a5505eefef5c8198fe184ed5ac
-F ext/misc/shathree.c 135b7c145db4a09b1650c3e7aff9cb538763a9a361e834c015dd1aaf8d5c9a00
+F ext/misc/shathree.c 86bee126b89dc7f3a9edc6d31497588a0f1e78ab867025a766b67f52bcf1f656
 F ext/misc/showauth.c 732578f0fe4ce42d577e1c86dc89dd14a006ab52
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 F ext/misc/sqlar.c 0ace5d3c10fe736dc584bf1159a36b8e2e60fab309d310cd8a0eecd9036621b6
@@ -462,7 +463,7 @@ F ext/userauth/userauth.c 7f00cded7dcaa5d47f54539b290a43d2e59f4b1eb5f447545fa865
 F install-sh 9d4de14ab9fb0facae2f48780b874848cbf2f895 x
 F ltmain.sh 3ff0879076df340d2e23ae905484d8c15d5fdea8
 F magic.txt 8273bf49ba3b0c8559cb2774495390c31fd61c60
-F main.mk 57451ea5b3d5cd86e9c5324b10c9de184b12e8dcccc31c65d24fbcb55ccd9c53
+F main.mk 4e4d6ff9cc79b84c724d8d529474b6ca54215b22758da9cbd620646edeb784a6
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 F mptest/config02.test 4415dfe36c48785f751e16e32c20b077c28ae504
@@ -474,9 +475,9 @@ F spec.template 86a4a43b99ebb3e75e6b9a735d5fd293a24e90ca
 F sqlite.pc.in 42b7bf0d02e08b9e77734a47798d1a55a9e0716b
 F sqlite3.1 fc7ad8990fc8409983309bb80de8c811a7506786
 F sqlite3.pc.in 48fed132e7cb71ab676105d2a4dc77127d8c1f3a
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-F src/attach.c 0f497c15c4cfe3bdcb214f0dbdbbb6c5ed7e8a9308ac445c7959f5e5780437a9
+F src/alter.c 5f81b936ed65586ae57d126b16ed928e336d6f99df09a700b3d96a0ebb99068a
+F src/analyze.c 8b522a57784406d75f544e6d67f3fe7a7196702d3d954b7678bb4b4fe789e5a4
+F src/attach.c 2fb83ab273c2f8df9511c8b12f0c70f99712d8bbda87a40bbfcd810af7594a14
 F src/auth.c a3d5bfdba83d25abed1013a8c7a5f204e2e29b0c25242a56bc02bb0c07bf1e06
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 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
@@ -484,17 +485,17 @@ F src/btmutex.c 8acc2f464ee76324bf13310df5692a262b801808984c1b79defb2503bbafadb6
 F src/btree.c ee14224322b9e4172d01e691e2f289f6c630ae39b7906f84b72dc780b9e42a76
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 F src/btreeInt.h ffd66480520d9d70222171b3a026d78b80833b5cea49c89867949f3e023d5f43
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-F src/callback.c d0b853dd413255d2e337b34545e54d888ea02f20da5ad0e63585b389624c4a6c
+F src/build.c 33e7b9f5d7c574148d54fe62fd997341adc3d411a3fae42e5aaa3528214ef238
+F src/callback.c d8cdf5d697a31cf54a2b64bce9001fe24f3522a566f44c9fe1eb3a0c7e291c56
 F src/complete.c a3634ab1e687055cd002e11b8f43eb75c17da23e
-F src/ctime.c e98518d2d3d4029a13c805e07313fb60c877be56db76e90dd5f3af73085d0ce6
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-F src/fkey.c 83372403298e6a7dd989a47aaacdbaa5b4307b5199dbd56e07d4896066b3de72
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@@ -504,7 +505,7 @@ F src/in-operator.md 10cd8f4bcd225a32518407c2fb2484089112fd71
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@@ -533,23 +534,23 @@ F src/parse.y 9ce4dfb772608ed5bd3c32f33e943e021e3b06cfd2c01932d4280888fdd2ebed
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+F src/status.c d0956e57c71160155f620a3efeb1e5c05a3f8b9a897dd09c5263268e5d237579
 F src/table.c 0f141b58a16de7e2fbe81c308379e7279f4c6b50eb08efeec5892794a0ba30d1
-F src/tclsqlite.c 986b6391f02cd9b53c1d688be55899f6ffddeb8e8014cd83c1b73ff912579a71
+F src/tclsqlite.c f4dd32d001c2be33371dca87e30117352f02dad59a2e5428c97f08703360a169
 F src/test1.c 2197966d2f7211ef9eefaa6c3c7dd2c7d786d1f33f2aadef2f08c8c79eceec26
 F src/test2.c 3efb99ab7f1fc8d154933e02ae1378bac9637da5
 F src/test3.c 61798bb0d38b915067a8c8e03f5a534b431181f802659a6616f9b4ff7d872644
@@ -565,7 +566,7 @@ F src/test_backup.c bf5da90c9926df0a4b941f2d92825a01bbe090a0
 F src/test_bestindex.c 78809f11026f18a93fcfd798d9479cba37e1201c830260bf1edc674b2fa9b857
 F src/test_blob.c ae4a0620b478548afb67963095a7417cd06a4ec0a56adb453542203bfdcb31ce
 F src/test_btree.c 8b2dc8b8848cf3a4db93f11578f075e82252a274
-F src/test_config.c 5ea19bf0972a9d91728518b4d30e91477acce80496003ecbef3a7fb18d0bd081
+F src/test_config.c 9eaeaa599673b8e8732b80540549250a1f1b5bab5de4bfd76b1566f495bc95ab
 F src/test_delete.c e2fe07646dff6300b48d49b2fee2fe192ed389e834dd635e3b3bac0ce0bf9f8f
 F src/test_demovfs.c 86142ba864d4297d54c5b2e972e74f3141ae4b30f05b3a95824184ed2d3d7f91
 F src/test_devsym.c aff2255ea290d7718da08af30cdf18e470ff7325a5eff63e0057b1496ed66593
@@ -589,11 +590,12 @@ F src/test_quota.c 6cb9297115b551f433a9ad1741817a9831abed99
 F src/test_quota.h 2a8ad1952d1d2ca9af0ce0465e56e6c023b5e15d
 F src/test_rtree.c 671f3fae50ff116ef2e32a3bf1fe21b5615b4b7b
 F src/test_schema.c f5d6067dfc2f2845c4dd56df63e66ee826fb23877855c785f75cc2ca83fd0c1b
+F src/test_schemapool.c ae21a79f9bc7e9099ae78dbd46d5c28ee75330e62e3256a9fde25564ff9df492
 F src/test_server.c a2615049954cbb9cfb4a62e18e2f0616e4dc38fe
 F src/test_sqllog.c 540feaea7280cd5f926168aee9deb1065ae136d0bbbe7361e2ef3541783e187a
 F src/test_superlock.c 4839644b9201da822f181c5bc406c0b2385f672e
 F src/test_syscall.c 1073306ba2e9bfc886771871a13d3de281ed3939
-F src/test_tclsh.c eeafce33ad2136d57e5dec10f1e9a4347447eb72ffd504a1c7b9c6bfe2e71578
+F src/test_tclsh.c 6cbaaf30c4fed76c7b35baa42c521fd225c49563ff580f736d77def9e216b31b
 F src/test_tclvar.c 33ff42149494a39c5fbb0df3d25d6fafb2f668888e41c0688d07273dcb268dfc
 F src/test_thread.c 269ea9e1fa5828dba550eb26f619aa18aedbc29fd92f8a5f6b93521fbb74a61c
 F src/test_vdbecov.c f60c6f135ec42c0de013a1d5136777aa328a776d33277f92abac648930453d43
@@ -604,25 +606,25 @@ F src/test_windirent.h 90dfbe95442c9762357fe128dc7ae3dc199d006de93eb33ba3972e0a9
 F src/test_window.c cdae419fdcea5bad6dcd9368c685abdad6deb59e9fc8b84b153de513d394ba3f
 F src/test_wsd.c 41cadfd9d97fe8e3e4e44f61a4a8ccd6f7ca8fe9
 F src/threads.c 4ae07fa022a3dc7c5beb373cf744a85d3c5c6c3c
-F src/tokenize.c 01dba3023659dc6f6b1e054c14b35a0074bd35de10466b99454d33278191d97f
+F src/tokenize.c 369a8ef43e4e3ef2818ad6cf6ef7b167973fc297ca93af4dfab4453db214ec3e
 F src/treeview.c 4b92992176fb2caefbe06ba5bd06e0e0ebcde3d5564758da672631f17aa51cda
-F src/trigger.c 515e79206d40d1d4149129318582e79a6e9db590a7b74e226fdb5b2a6c7e1b10
+F src/trigger.c e9eb8ceb72f852057951b1bfb94be677573682f49c77aab13e3e5a3dd36f3f91
 F src/update.c 9f126204a6acb96bbe47391ae48e0fc579105d8e76a6d9c4fab3271367476580
 F src/upsert.c 2920de71b20f04fe25eb00b655d086f0ba60ea133c59d7fa3325c49838818e78
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
 F src/util.c c0c7977de7ef9b8cb10f6c85f2d0557889a658f817b0455909a49179ba4c8002
-F src/vacuum.c 492422c1463c076473bae1858799c7a0a5fe87a133d1223239447c422cd26286
-F src/vdbe.c d24a43b6b1ed2dba893636a14f5e56001444ab3fd5465e3bca8ab01799840acd
-F src/vdbe.h 83603854bfa5851af601fc0947671eb260f4363e62e960e8a994fb9bbcd2aaa1
+F src/vacuum.c 724188c5afbba905b310e8d8e78530956d16e6d60a3ba8a1105d05732d7d8601
+F src/vdbe.c 05d7dbe213ee570e33e89fb34f9bcfd9926bb9f7b1cf2fd9a65b5e3a2e83e950
+F src/vdbe.h 9e947bd4a40e3b65159b699571c8246c209f6bda6e13979a1ab623faa2f0d23f
 F src/vdbeInt.h 3ca5e9fd6e095a8b6cf6bc3587a46fc93499503b2fe48951e1034ba9e2ce2f6e
 F src/vdbeapi.c c5e7cb2ab89a24d7f723e87b508f21bfb1359a04db5277d8a99fd1e015c12eb9
-F src/vdbeaux.c c76b7e96e189f5056d1de914d33d07bd03d3b88741f75375c8e18c9b11ffd379
-F src/vdbeblob.c 253ed82894924c362a7fa3079551d3554cd1cdace39aa833da77d3bc67e7c1b1
+F src/vdbeaux.c 533d41dab3537c81727142af61a409797f5922d474504ec6123e4819e7d1e538
+F src/vdbeblob.c 40028e015fe557a945c99edb6cbf844ea96d853c3e8ac4eb5c1e49bff59f154e
 F src/vdbemem.c 947f2a65910edb4014dc981d33e414a68c51f169f9df8c4c493a0ba840b6eb1f
 F src/vdbesort.c f5b5e473a7cee44e47a94817b042fd7172cf3aa2c0a7928a8339d612bcfdec5a
 F src/vdbetrace.c fa3bf238002f0bbbdfb66cc8afb0cea284ff9f148d6439bc1f6f2b4c3b7143f0
 F src/vdbevtab.c f99b275366c5fc5e2d99f734729880994ab9500bdafde7fae3b02d562b9d323c
-F src/vtab.c 5f5fc793092f53bbdfde296c50f563fb7bda58cf48e9cf6a8bdfbc5abd409845
+F src/vtab.c 54b6ab9f5ab772f56e9f3a95543207943e775ec699b7cbbfd3a99c264cad377f
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c 69e770e96fd56cc21608992bf2c6f1f3dc5cf2572d0495c6a643b06c3a679f14
 F src/wal.h c3aa7825bfa2fe0d85bef2db94655f99870a285778baa36307c0a16da32b226a
@@ -1048,7 +1050,7 @@ F test/fuzzerfault.test 8792cd77fd5bce765b05d0c8e01b9edcf8af8536
 F test/gcfault.test dd28c228a38976d6336a3fc42d7e5f1ad060cb8c
 F test/gencol1.test b05e6c5edb9b10d48efb634ed07342441bddc89d225043e17095c36e567521a0
 F test/genesis.tcl 1e2e2e8e5cc4058549a154ff1892fe5c9de19f98
-F test/having.test e4098a4b8962f9596035c3b87a8928a10648acc509f1bb8d6f96413bbf79a1b3
+F test/having.test ea5cb01cdf3d90fd1b516ef36b1fbde518dbbd61c50141f5eb830d8101844040
 F test/hexlit.test 4a6a5f46e3c65c4bf1fa06f5dd5a9507a5627751
 F test/hidden.test 23c1393a79e846d68fd902d72c85d5e5dcf98711
 F test/hook.test e97382e68e4379838e888756d653afd159f5f14780315ff97b70360d3d8485bc
@@ -1281,6 +1283,13 @@ F test/releasetest.tcl fb76d8fcc95ac29d6356cd9e52b726ab9e43a24082897618dfbcb7c2b
 F test/releasetest_data.tcl b9cb30360759b80d92d4ea86b84ebfd8035b97f9078a482deb3cf9d0b2442655
 F test/resetdb.test 8062cf10a09d8c048f8de7711e94571c38b38168db0e5877ba7561789e5eeb2b
 F test/resolver01.test f4022acafda7f4d40eca94dbf16bc5fc4ac30ceb
+F test/reuse1.test faa2ce5ff566d936b8a10d9e22ba2ee66a54ce89fdcf8aef561df6b15b0ff3d3
+F test/reuse2.test 5dd9c98579358f0d5a90d25e36dd6e678a03e23446b6c7f2630a8da22ae7ca94
+F test/reuse3.test 876d15c42d61b1f6ab718cd8169912514ad314d7fe1cd9788080aa62168ba0d1
+F test/reuse4.test adaad66253aea6cc748674328abe69b650c5c78b8676ed1162d3de09742519f9
+F test/reuse5.test bbe6cf7384ef90f134392edd93d626385ef0bf6f40eefc3d993535cd0861d83b
+F test/reuse6.test f4674f9967aee2a0b49c02832120b8b495291c0d87aae084c54e6c0cc18132fe
+F test/reusefault.test ef646a0fb51d50ddfb4b7cd872f88e7d36eaba64bde7797b3418c3774e1c8d14
 F test/rollback.test 06680159bc6746d0f26276e339e3ae2f951c64812468308838e0a3362d911eaa
 F test/rollback2.test bc868d57899dc6972e2b4483faae0e03365a0556941474eec487ae21d8d38bb6
 F test/rollbackfault.test 0e646aeab8840c399cfbfa43daab46fd609cf04a
@@ -1424,7 +1433,7 @@ F test/tabfunc01.test 5ca6d004157a3e886a55a9387b960cc0db41acd88753eb597ff409ec6c
 F test/table.test eb3463b7add9f16a5bb836badf118cf391b809d09fdccd1f79684600d07ec132
 F test/tableapi.test ecbcc29c4ab62c1912c3717c48ea5c5e59f7d64e4a91034e6148bd2b82f177f4
 F test/tableopts.test dba698ba97251017b7c80d738c198d39ab747930
-F test/tclsqlite.test 79a473f5797e317c08f2c4f8192edb3eea6a67329b1087453328b66a7cb31070
+F test/tclsqlite.test 9ad3f8d337ae8e460b25d82094ff1b4f180afc3ca73856ec5a90ac215f43906c
 F test/tempdb.test 4cdaa23ddd8acb4d79cbb1b68ccdfd09b0537aaba909ca69a876157c2a2cbd08
 F test/tempdb2.test 353864e96fd3ae2f70773d0ffbf8b1fe48589b02c2ec05013b540879410c3440
 F test/tempfault.test 0c0d349c9a99bf5f374655742577f8712c647900
@@ -1443,7 +1452,7 @@ F test/thread2.test f35d2106452b77523b3a2b7d1dcde2e5ee8f9e46
 F test/thread_common.tcl 334639cadcb9f912bf82aa73f49efd5282e6cadd
 F test/threadtest1.c 6029d9c5567db28e6dc908a0c63099c3ba6c383b
 F test/threadtest2.c a70a8e94bef23339d34226eb9521015ef99f4df8
-F test/threadtest3.c e63013af10cf236c7610eb06d33bde08c861806dc64be811940ff4d9ddd34a4f
+F test/threadtest3.c e58f0e1b6a3e4ccb24f831650c296e800f6299cc258793f6fc372591f416cb93
 F test/threadtest4.c c1e67136ceb6c7ec8184e56ac61db28f96bd2925
 F test/time-wordcount.sh 8e0b0f8109367827ad5d58f5cc849705731e4b90
 F test/tkt-02a8e81d44.test 6c80d9c7514e2a42d4918bf87bf6bc54f379110c
@@ -1616,12 +1625,13 @@ F test/triggerF.test 5d76f0a8c428ff87a4d5ed52da06f6096a2c787a1e21b846111dfac4123
 F test/triggerG.test 2b816093c91ba73c733cfa8aedcc210ad819d72a98b1da30768a3c56505233e9
 F test/triggerupfrom.test d25961fa70a99b6736193da7b49a36d8c1d28d56188f0be6406d4366315cd6e4
 F test/trustschema1.test 4e970aef0bfe0cee139703cc7209d0e0f07725d999b180ba50770f49edef1494
-F test/tt3_checkpoint.c 9e75cf7c1c364f52e1c47fd0f14c4340a9db0fe1
-F test/tt3_index.c 39eec10a35f57672225be4d182862152896dee4a
-F test/tt3_lookaside1.c 0377e202c3c2a50d688cb65ba203afeda6fafeb9
+F test/tt3_checkpoint.c 9a7fe00e07700af027769d83ef67ab727927ae6c865ecdc71fe8011194200c53
+F test/tt3_index.c 95592839426dc85ce5a7a57b41be2cbf3c2ec3457b9cd841a06ed5877f712c7c
+F test/tt3_lookaside1.c 2ddd99bfffeef288f0786827ef68f912f6f47ce3d3184e62f05808d8e13b920e
+F test/tt3_reuseschema.c 4d52e141f89f009028d8ab0bd1f0697d0edffa94bafc1fff0f7ad4d9d9baa549
 F test/tt3_shared.c b37d22defc944a2ac4c91c927fd06c1d48cd51e2ce9d004fe868625bd2399f93
-F test/tt3_stress.c f9a769ca8b026ecc76ee93ca8c9700a5619f8e51c581107c4053ba6ac97f616f
-F test/tt3_vacuum.c 1753f45917699c9c1f66b64c717a717c9379f776
+F test/tt3_stress.c 077e817ac1168443b075fedb44e92db84bb4dc5bd3b6fe1aba25c94ac280b231
+F test/tt3_vacuum.c ca42adcf8a671abbe34338b828464269e21758a6b4857b889dabfd39a3206d98
 F test/types.test bf816ce73c7dfcfe26b700c19f97ef4050d194ff
 F test/types2.test 1aeb81976841a91eef292723649b5c4fe3bc3cac
 F test/types3.test 99e009491a54f4dc02c06bdbc0c5eea56ae3e25a
@@ -1820,7 +1830,7 @@ F tool/mkmsvcmin.tcl 6ecab9fe22c2c8de4d82d4c46797bda3d2deac8e763885f5a38d0c44a89
 F tool/mkopcodec.tcl d1b6362bd3aa80d5520d4d6f3765badf01f6c43c
 F tool/mkopcodeh.tcl 352a4319c0ad869eb26442bf7c3b015aa15594c21f1cce5a6420dbe999367c21
 F tool/mkopts.tcl 680f785fdb09729fd9ac50632413da4eadbdf9071535e3f26d03795828ab07fa
-F tool/mkpragmatab.tcl ae5585ae76ca26e4d6ccd5ea9cdebaf5efefb318bf989497a0e846cd711d9ab1
+F tool/mkpragmatab.tcl 37381569b5a5cd3269e3fdbc08829eb1a5f7c2a8e59ee7be8995127e5ef99e0d
 F tool/mkshellc.tcl 70a9978e363b0f3280ca9ce1c46d72563ff479c1930a12a7375e3881b7325712
 F tool/mksourceid.c 36aa8020014aed0836fd13c51d6dc9219b0df1761d6b5f58ff5b616211b079b9
 F tool/mkspeedsql.tcl a1a334d288f7adfe6e996f2e712becf076745c97
@@ -1887,7 +1897,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P fd02dffceb0e21cd85c99d5481ab8567110d01c30ea701178547f32299944302
-R d3c2d5d830919ec315662cc1d113703f
+P 846e8444f761a4f3e3e0fb89e87b329799a6e8dd32ac7580dc20eb6ff9ed0d36 10e20c0b43500cfb9bbc0eaa061c57514f715d87238f4d835880cd846b9ebd1f
+R c3bca53baf6ecb114d5b954d3fbf96c3
+T *branch * reuse-schema-3.34
+T *sym-reuse-schema-3.34 *
+T -sym-reuse-schema *
 U drh
-Z d16f9ab88139a6919756f891af8788a5
+Z d7f43de9fad3ffe4577da84774a1c766
@@ -1 +1 @@
-1db7c751912beb57a697ac8e85b9c29e30da7b6c89207e9828bf08e56c58242f
+cc0e582854be11c29186d535130344c5486deb124ec4135a50ee1de21ea44a1d
@@ -80,8 +80,8 @@ static void renameReloadSchema(Parse *pParse, int iDb){
  Vdbe *v = pParse->pVdbe;
  if( v ){
    sqlite3ChangeCookie(pParse, iDb);
-    sqlite3VdbeAddParseSchemaOp(pParse->pVdbe, iDb, 0);
-    if( iDb!=1 ) sqlite3VdbeAddParseSchemaOp(pParse->pVdbe, 1, 0);
+    sqlite3VdbeAddParseSchemaOp(pParse, iDb, 0);
+    if( iDb!=1 ) sqlite3VdbeAddParseSchemaOp(pParse, 1, 0);
  }
 }

@@ -212,6 +212,7 @@ static void openStatTable(
        ** side-effect of the CREATE TABLE statement is to leave the rootpage 
        ** of the new table in register pParse->regRoot. This is important 
        ** because the OpenWrite opcode below will be needing it. */
+        sqlite3SchemaWritable(pParse, iDb);
        sqlite3NestedParse(pParse,
            "CREATE TABLE %Q.%s(%s)", pDb->zDbSName, zTab, aTable[i].zCols
        );
@@ -205,14 +205,14 @@ static void attachFunc(
  ** way we found it.
  */
  if( rc==SQLITE_OK ){
-    sqlite3BtreeEnterAll(db);
    db->init.iDb = 0;
    db->mDbFlags &= ~(DBFLAG_SchemaKnownOk);
-    if( !REOPEN_AS_MEMDB(db) ){
+    if( !IsSharedSchema(db) && !REOPEN_AS_MEMDB(db) ){
+      sqlite3BtreeEnterAll(db);
      rc = sqlite3Init(db, &zErrDyn);
+      sqlite3BtreeLeaveAll(db);
+      assert( zErrDyn==0 || rc!=SQLITE_OK );
    }
-    sqlite3BtreeLeaveAll(db);
-    assert( zErrDyn==0 || rc!=SQLITE_OK );
  }
 #ifdef SQLITE_USER_AUTHENTICATION
  if( rc==SQLITE_OK && !REOPEN_AS_MEMDB(db) ){
@@ -312,6 +312,7 @@ static void detachFunc(
    pEntry = sqliteHashNext(pEntry);
  }

+  sqlite3SchemaDisconnect(db, i, 0);
  sqlite3BtreeClose(pDb->pBt);
  pDb->pBt = 0;
  pDb->pSchema = 0;
@@ -295,6 +295,39 @@ int sqlite3UserAuthTable(const char *zTable){
 }
 #endif

+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+/*
+** If this database connection was opened with the SQLITE_OPEN_SHARED_SCHEMA
+** flag specified, then ensure that the database schema for database iDb
+** is loaded. Either by obtaining a Schema object from the schema-pool, or
+** by reading the contents of the sqlite_master table. Unless it is NULL, 
+** the location indicated by parameter pbUnload is set to 1 if a shared-schema 
+** is loaded.
+**
+** If the database handle was not opened with SQLITE_OPEN_SHARED_SCHEMA, or
+** if the schema for database iDb is already loaded, this function is a no-op.
+**
+** SQLITE_OK is returned if successful, or an SQLite error code otherwise. If
+** an error code is returned, (*pzErr) may be set to point to a buffer
+** containing an error message. It is the responsibility of the caller to
+** eventually free this buffer using sqlite3_free().
+*/
+int sqlite3SchemaLoad(sqlite3 *db, int iDb, int *pbUnload, char **pzErr){
+  int rc = SQLITE_OK;
+  if( IsSharedSchema(db) 
+      && DbHasProperty(db, iDb, DB_SchemaLoaded)==0 
+      && (db->init.busy==0 || (iDb!=1 && db->init.iDb==1))
+  ){
+    struct sqlite3InitInfo sv = db->init;
+    memset(&db->init, 0, sizeof(struct sqlite3InitInfo));
+    rc = sqlite3InitOne(db, iDb, pzErr, 0);
+    db->init = sv;
+    if( pbUnload && rc==SQLITE_OK && iDb!=1 ) *pbUnload = 1;
+  }
+  return rc;
+}
+#endif
+
 /*
 ** Locate the in-memory structure that describes a particular database
 ** table given the name of that table and (optionally) the name of the
@@ -320,59 +353,41 @@ Table *sqlite3FindTable(sqlite3 *db, const char *zName, const char *zDatabase){
    return 0;
  }
 #endif
-  if( zDatabase ){
-    for(i=0; i<db->nDb; i++){
-      if( sqlite3StrICmp(zDatabase, db->aDb[i].zDbSName)==0 ) break;
-    }
-    if( i>=db->nDb ){
-      /* No match against the official names.  But always match "main"
-      ** to schema 0 as a legacy fallback. */
-      if( sqlite3StrICmp(zDatabase,"main")==0 ){
-        i = 0;
-      }else{
-        return 0;
-      }
-    }
-    p = sqlite3HashFind(&db->aDb[i].pSchema->tblHash, zName);
-    if( p==0 && sqlite3StrNICmp(zName, "sqlite_", 7)==0 ){
-      if( i==1 ){
-        if( sqlite3StrICmp(zName+7, &ALT_TEMP_SCHEMA_TABLE[7])==0
-         || sqlite3StrICmp(zName+7, &ALT_SCHEMA_TABLE[7])==0
-         || sqlite3StrICmp(zName+7, &DFLT_SCHEMA_TABLE[7])==0
-        ){
-          p = sqlite3HashFind(&db->aDb[1].pSchema->tblHash, 
-                              DFLT_TEMP_SCHEMA_TABLE);
+  while(1){
+    for(i=OMIT_TEMPDB; i<db->nDb; i++){
+      int j = (i<2) ? i^1 : i;   /* Search TEMP before MAIN */
+      if( zDatabase==0 || sqlite3DbIsNamed(db, j, zDatabase) ){
+        int bUnload = 0;
+        assert( sqlite3SchemaMutexHeld(db, j, 0) );
+        if( IsSharedSchema(db) ){
+          Parse *pParse = db->pParse;
+          if( pParse && pParse->nErr==0 ){
+            pParse->rc = sqlite3SchemaLoad(db, j, &bUnload, &pParse->zErrMsg);
+            if( pParse->rc ) pParse->nErr++;
+          }
        }
-      }else{
-        if( sqlite3StrICmp(zName+7, &ALT_SCHEMA_TABLE[7])==0 ){
-          p = sqlite3HashFind(&db->aDb[i].pSchema->tblHash,
-                              DFLT_SCHEMA_TABLE);
+        p = sqlite3HashFind(&db->aDb[j].pSchema->tblHash, zName);
+        if( p ) return p;
+        if( bUnload ){
+          sqlite3SchemaRelease(db, j);
        }
      }
    }
-  }else{
-    /* Match against TEMP first */
-    p = sqlite3HashFind(&db->aDb[1].pSchema->tblHash, zName);
-    if( p ) return p;
-    /* The main database is second */
-    p = sqlite3HashFind(&db->aDb[0].pSchema->tblHash, zName);
-    if( p ) return p;
-    /* Attached databases are in order of attachment */
-    for(i=2; i<db->nDb; i++){
-      assert( sqlite3SchemaMutexHeld(db, i, 0) );
-      p = sqlite3HashFind(&db->aDb[i].pSchema->tblHash, zName);
-      if( p ) break;
+    /* Not found.  If the name we were looking for was temp.sqlite_master
+    ** then change the name to sqlite_temp_master and try again. */
+    if( sqlite3StrICmp(zName, ALT_SCHEMA_TABLE)==0 ){
+      zName = DFLT_SCHEMA_TABLE;
+      continue;
    }
-    if( p==0 && sqlite3StrNICmp(zName, "sqlite_", 7)==0 ){
-      if( sqlite3StrICmp(zName+7, &ALT_SCHEMA_TABLE[7])==0 ){
-        p = sqlite3HashFind(&db->aDb[0].pSchema->tblHash, DFLT_SCHEMA_TABLE);
-      }else if( sqlite3StrICmp(zName+7, &ALT_TEMP_SCHEMA_TABLE[7])==0 ){
-        p = sqlite3HashFind(&db->aDb[1].pSchema->tblHash, 
-                            DFLT_TEMP_SCHEMA_TABLE);
-      }
+    if( sqlite3StrICmp(zName, ALT_TEMP_SCHEMA_TABLE)==0 ){
+      zName = DFLT_TEMP_SCHEMA_TABLE;
+      continue;
    }
+    if( sqlite3StrICmp(zName, DFLT_SCHEMA_TABLE)!=0 ) break;
+    if( sqlite3_stricmp(zDatabase, db->aDb[1].zDbSName)!=0 ) break;
+    zName = DFLT_TEMP_SCHEMA_TABLE;
  }
-  return p;
+  return 0;
 }

 /*
@@ -397,6 +412,7 @@ Table *sqlite3LocateTable(
  /* Read the database schema. If an error occurs, leave an error message
  ** and code in pParse and return NULL. */
  if( (db->mDbFlags & DBFLAG_SchemaKnownOk)==0 
+   && !IsSharedSchema(db)
   && SQLITE_OK!=sqlite3ReadSchema(pParse)
  ){
    return 0;
@@ -413,8 +429,18 @@ Table *sqlite3LocateTable(
      if( pMod==0 && sqlite3_strnicmp(zName, "pragma_", 7)==0 ){
        pMod = sqlite3PragmaVtabRegister(db, zName);
      }
-      if( pMod && sqlite3VtabEponymousTableInit(pParse, pMod) ){
-        return pMod->pEpoTab;
+      if( pMod ){
+        if( IsSharedSchema(db) && pParse->nErr==0 ){
+          int bDummy = 0;
+          pParse->rc = sqlite3SchemaLoad(db, 0, &bDummy, &pParse->zErrMsg);
+          if( pParse->rc ) pParse->nErr++;
+        }
+        if( sqlite3VtabEponymousTableInit(pParse, pMod) ){
+          Table *pEpoTab = pMod->pEpoTab;
+          assert( IsSharedSchema(db) || pEpoTab->pSchema==db->aDb[0].pSchema );
+          pEpoTab->pSchema = db->aDb[0].pSchema;  /* For SHARED_SCHEMA mode */
+          return pEpoTab;
+        }
      }
    }
 #endif
@@ -424,7 +450,7 @@ Table *sqlite3LocateTable(
    p = 0;
  }

-  if( p==0 ){
+  if( p==0 && (!IsSharedSchema(db) || pParse->nErr==0) ){
    const char *zMsg = flags & LOCATE_VIEW ? "no such view" : "no such table";
    if( zDbase ){
      sqlite3ErrorMsg(pParse, "%s: %s.%s", zMsg, zDbase, zName);
@@ -583,11 +609,10 @@ void sqlite3ResetOneSchema(sqlite3 *db, int iDb){
    DbSetProperty(db, 1, DB_ResetWanted);
    db->mDbFlags &= ~DBFLAG_SchemaKnownOk;
  }
-
  if( db->nSchemaLock==0 ){
    for(i=0; i<db->nDb; i++){
      if( DbHasProperty(db, i, DB_ResetWanted) ){
-        sqlite3SchemaClear(db->aDb[i].pSchema);
+        sqlite3SchemaClearOrDisconnect(db, i);
      }
    }
  }
@@ -600,16 +625,17 @@ void sqlite3ResetOneSchema(sqlite3 *db, int iDb){
 void sqlite3ResetAllSchemasOfConnection(sqlite3 *db){
  int i;
  sqlite3BtreeEnterAll(db);
-  for(i=0; i<db->nDb; i++){
+  for(i=0; i<db->nDb; i=(i?i+1:2)){
    Db *pDb = &db->aDb[i];
    if( pDb->pSchema ){
      if( db->nSchemaLock==0 ){
-        sqlite3SchemaClear(pDb->pSchema);
+        sqlite3SchemaClearOrDisconnect(db, i);
      }else{
        DbSetProperty(db, i, DB_ResetWanted);
      }
    }
  }
+  sqlite3SchemaClear(db->aDb[1].pSchema);
  db->mDbFlags &= ~(DBFLAG_SchemaChange|DBFLAG_SchemaKnownOk);
  sqlite3VtabUnlockList(db);
  sqlite3BtreeLeaveAll(db);
@@ -1105,7 +1131,7 @@ void sqlite3StartTable(
  */
  if( !IN_SPECIAL_PARSE ){
    char *zDb = db->aDb[iDb].zDbSName;
-    if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
+    if( !IsSharedSchema(db) && SQLITE_OK!=sqlite3ReadSchema(pParse) ){
      goto begin_table_error;
    }
    pTable = sqlite3FindTable(db, zName, zDb);
@@ -2533,7 +2559,7 @@ void sqlite3EndTable(
 #endif

    /* Reparse everything to update our internal data structures */
-    sqlite3VdbeAddParseSchemaOp(v, iDb,
+    sqlite3VdbeAddParseSchemaOp(pParse, iDb,
           sqlite3MPrintf(db, "tbl_name='%q' AND type!='trigger'", p->zName));
  }

@@ -3065,7 +3091,7 @@ void sqlite3DropTable(Parse *pParse, SrcList *pName, int isView, int noErr){
  }
  assert( pParse->nErr==0 );
  assert( pName->nSrc==1 );
-  if( sqlite3ReadSchema(pParse) ) goto exit_drop_table;
+  if( !IsSharedSchema(db) && sqlite3ReadSchema(pParse) ) goto exit_drop_table;
  if( noErr ) db->suppressErr++;
  assert( isView==0 || isView==LOCATE_VIEW );
  pTab = sqlite3LocateTableItem(pParse, isView, &pName->a[0]);
@@ -3077,6 +3103,7 @@ void sqlite3DropTable(Parse *pParse, SrcList *pName, int isView, int noErr){
  }
  iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
  assert( iDb>=0 && iDb<db->nDb );
+  sqlite3SchemaWritable(pParse, iDb);

  /* If pTab is a virtual table, call ViewGetColumnNames() to ensure
  ** it is initialized.
@@ -3525,7 +3552,7 @@ void sqlite3CreateIndex(
  if( IN_DECLARE_VTAB && idxType!=SQLITE_IDXTYPE_PRIMARYKEY ){
    goto exit_create_index;
  }
-  if( SQLITE_OK!=sqlite3ReadSchema(pParse) ){
+  if( !IsSharedSchema(db) && SQLITE_OK!=sqlite3ReadSchema(pParse) ){
    goto exit_create_index;
  }
  if( sqlite3HasExplicitNulls(pParse, pList) ){
@@ -4021,7 +4048,7 @@ void sqlite3CreateIndex(
      if( pTblName ){
        sqlite3RefillIndex(pParse, pIndex, iMem);
        sqlite3ChangeCookie(pParse, iDb);
-        sqlite3VdbeAddParseSchemaOp(v, iDb,
+        sqlite3VdbeAddParseSchemaOp(pParse, iDb,
            sqlite3MPrintf(db, "name='%q' AND type='index'", pIndex->zName));
        sqlite3VdbeAddOp2(v, OP_Expire, 0, 1);
      }
@@ -4156,6 +4183,7 @@ void sqlite3DropIndex(Parse *pParse, SrcList *pName, int ifExists){
    goto exit_drop_index;
  }
  iDb = sqlite3SchemaToIndex(db, pIndex->pSchema);
+  sqlite3SchemaWritable(pParse, iDb);
 #ifndef SQLITE_OMIT_AUTHORIZATION
  {
    int code = SQLITE_DROP_INDEX;
@@ -16,6 +16,63 @@

 #include "sqliteInt.h"

+/*
+** Connections opened with the SQLITE_OPEN_SHARED_SCHEMA flag specified
+** may use SchemaPool objects for any database that is not the temp db
+** (iDb==1). For such databases (type "struct Db") there are three states
+** the Schema/SchemaPool object may be in.
+**
+**   1) pSPool==0, pSchema points to an empty object allocated by
+**      sqlite3_malloc(). DB_SchemaLoaded flag is clear.
+**
+**   2) pSPool!=0, pSchema points to a populated object owned by the
+**      SchemaPool. DB_SchemaLoaded flag is set.
+**
+**   3) pSPool!=0, pSchema points to the SchemaPool's static object
+**      (SchemaPool.sSchema).
+*/
+struct SchemaPool {
+  int nRef;                       /* Number of pointers to this object */
+  int nDelete;                    /* Schema objects deleted by ReleaseAll() */
+  u64 cksum;                      /* Checksum for this Schema contents */
+  Schema *pSchema;                /* Linked list of Schema objects */
+  Schema sSchema;                 /* The single dummy schema object */
+  SchemaPool *pNext;              /* Next element in schemaPoolList */
+};
+
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+#ifdef SQLITE_DEBUG
+static void assert_schema_state_ok(sqlite3 *db){
+  if( IsSharedSchema(db) && db->magic!=SQLITE_MAGIC_ZOMBIE ){
+    int i;
+    for(i=0; i<db->nDb; i++){
+      if( i!=1 ){
+        Db *pDb = &db->aDb[i];
+        Btree *pBt = pDb->pBt;
+        if( pBt==0 ) continue;
+        assert( sqlite3BtreeSchema(pBt, 0, 0)==0 );
+        assert( pDb->pSchema );
+        if( pDb->pSPool ){
+          if( DbHasProperty(db, i, DB_SchemaLoaded)==0 ){
+            assert( pDb->pSchema->tblHash.count==0 );
+            assert( pDb->pSchema==&pDb->pSPool->sSchema );
+          }else{
+            assert( pDb->pSchema!=&pDb->pSPool->sSchema );
+          }
+        }else{
+          assert( DbHasProperty(db, i, DB_SchemaLoaded)==0 );
+          assert( pDb->pSchema->tblHash.count==0 );
+          assert( pDb->pSchema!=&pDb->pSPool->sSchema );
+        }
+      }
+    }
+  }
+}
+#else
+# define assert_schema_state_ok(x)
+#endif
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+
 /*
 ** Invoke the 'collation needed' callback to request a collation sequence
 ** in the encoding enc of name zName, length nName.
@@ -513,15 +570,317 @@ void sqlite3SchemaClear(void *p){
 }

 /*
-** Find and return the schema associated with a BTree.  Create
-** a new one if necessary.
+** If this database was opened with the SQLITE_OPEN_SHARED_SCHEMA flag
+** and iDb!=1, then disconnect from the schema-pool associated with
+** database iDb. Otherwise, clear the Schema object belonging to
+** database iDb. 
+**
+** If an OOM error occurs while disconnecting from a schema-pool, 
+** the db->mallocFailed flag is set.
+*/
+void sqlite3SchemaClearOrDisconnect(sqlite3 *db, int iDb){
+  Db *pDb = &db->aDb[iDb];
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  if( IsSharedSchema(db) && iDb!=1 && pDb->pSPool ){
+    sqlite3SchemaDisconnect(db, iDb, 1);
+  }else
+#endif
+  {
+    sqlite3SchemaClear(pDb->pSchema);
+  }
+}
+
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+/*
+** Global linked list of SchemaPool objects. Read and write access must
+** be protected by the SQLITE_MUTEX_STATIC_MASTER mutex.
+*/
+static SchemaPool *SQLITE_WSD schemaPoolList = 0;
+
+#ifdef SQLITE_TEST
+/*
+** Return a pointer to the head of the linked list of SchemaPool objects.
+** This is used by the virtual table in file test_schemapool.c.
+*/
+SchemaPool *sqlite3SchemaPoolList(void){ return schemaPoolList; }
+#endif
+
+/*
+** Database handle db was opened with the SHARED_SCHEMA flag, and database
+** iDb is currently connected to a schema-pool. When this function is called,
+** (*pnByte) is set to nInit plus the amount of memory used to store a 
+** single instance of the Schema objects managed by the schema-pool.
+** This function adjusts (*pnByte) sot hat it is set to nInit plus
+** (nSchema/nRef) of the amount of memory used by a single Schema object,
+** where nSchema is the number of Schema objects allocated by this pool,
+** and nRef is the number of connections to the schema-pool.
+*/
+void sqlite3SchemaAdjustUsed(sqlite3 *db, int iDb, int nInit, int *pnByte){
+  SchemaPool *pSPool = db->aDb[iDb].pSPool;
+  int nSchema = 0;
+  Schema *p;
+  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+  for(p=pSPool->pSchema; p; p=p->pNext){
+    nSchema++;
+  }
+  *pnByte = nInit + ((*pnByte - nInit) * nSchema) / pSPool->nRef;
+  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+}
+
+/*
+** Check that the schema of db iDb is writable (either because it is the 
+** temp db schema or because the db handle was opened without
+** SQLITE_OPEN_SHARED_SCHEMA). If so, do nothing. Otherwise, leave an 
+** error in the Parse object.
+*/
+void sqlite3SchemaWritable(Parse *pParse, int iDb){
+  if( iDb!=1 && IsSharedSchema(pParse->db) && IN_DECLARE_VTAB==0 ){
+    sqlite3ErrorMsg(pParse, "attempt to modify read-only schema");
+  }
+}
+
+/*
+** The schema object passed as the only argument was allocated using
+** sqlite3_malloc() and then populated using the usual mechanism. This
+** function frees both the Schema object and its contents.
+*/
+static void schemaDelete(Schema *pSchema){
+  sqlite3SchemaClear((void*)pSchema);
+  sqlite3_free(pSchema);
+}
+
+/*
+** When this function is called, the database connection Db must be
+** using a schema-pool (Db.pSPool!=0) and must currently have Db.pSchema
+** set to point to a populated schema object checked out from the 
+** schema-pool. It is also assumed that the STATIC_MASTER mutex is held.
+** This function returns the Schema object to the schema-pool and sets
+** Db.pSchema to point to the schema-pool's static, empty, Schema object.
+*/
+static void schemaRelease(sqlite3 *db, Db *pDb){
+  Schema *pRelease = pDb->pSchema;
+  SchemaPool *pSPool = pDb->pSPool;
+
+  assert( pDb->pSchema->iGeneration==pSPool->sSchema.iGeneration );
+  pDb->pSchema = &pSPool->sSchema;
+
+  assert( pDb->pSPool && pRelease );
+  assert( pRelease->schemaFlags & DB_SchemaLoaded );
+  assert( (pDb->pSchema->schemaFlags & DB_SchemaLoaded)==0 );
+  assert( sqlite3_mutex_held(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER)) );
+
+  /* If the DBFLAG_FreeSchema flag is set and the database connection holds
+  ** at least one other copy of the schema being released, delete it instead
+  ** of returning it to the schema-pool.  */
+  if( db->mDbFlags & DBFLAG_FreeSchema ){
+    int i;
+    for(i=0; i<db->nDb; i++){
+      Db *p = &db->aDb[i];
+      if( p!=pDb && p->pSchema!=&pSPool->sSchema && pDb->pSPool==p->pSPool ){
+        pSPool->nDelete++;
+        schemaDelete(pRelease);
+        return;
+      }
+    }
+  }
+
+  pRelease->pNext = pDb->pSPool->pSchema;
+  pDb->pSPool->pSchema = pRelease;
+}
+
+/*
+** The schema for database iDb of database handle db, which was opened
+** with SQLITE_OPEN_SHARED_SCHEMA, has just been parsed. This function either
+** finds a matching SchemaPool object on the global list (schemaPoolList) or
+** else allocates a new one and sets the Db.pSPool variable accordingly.
+**
+** SQLITE_OK is returned if no error occurs, or an SQLite error code 
+** (SQLITE_NOMEM) otherwise.
+*/
+int sqlite3SchemaConnect(sqlite3 *db, int iDb, u64 cksum){
+  Schema *pSchema = db->aDb[iDb].pSchema;
+  SchemaPool *p;
+
+  assert( pSchema && iDb!=1 && db->aDb[iDb].pSPool==0 );
+
+  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+
+  /* Search for a matching SchemaPool object */
+  for(p=schemaPoolList; p; p=p->pNext){
+    if( p->cksum==cksum && p->sSchema.schema_cookie==pSchema->schema_cookie ){
+      break;
+    }
+  }
+  if( !p ){
+    /* No SchemaPool object found. Allocate a new one. */
+    p = (SchemaPool*)sqlite3_malloc(sizeof(SchemaPool));
+    if( p ){
+      memset(p, 0, sizeof(SchemaPool));
+      p->cksum = cksum;
+      p->pNext = schemaPoolList;
+      schemaPoolList = p;
+
+      p->sSchema.schema_cookie = pSchema->schema_cookie;
+      p->sSchema.iGeneration = pSchema->iGeneration;
+      p->sSchema.file_format = pSchema->file_format;
+      p->sSchema.enc = pSchema->enc;
+      p->sSchema.cache_size = pSchema->cache_size;
+    }
+  }
+
+  if( p ) p->nRef++;
+
+  /* If the SchemaPool contains one or more free schemas at the moment, 
+  ** delete one of them. */
+  if( p && p->pSchema ){
+    Schema *pDel = p->pSchema;
+    p->pSchema = pDel->pNext;
+    schemaDelete(pDel);
+  }
+
+  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+
+  db->aDb[iDb].pSPool = p;
+  return (p ? SQLITE_OK : SQLITE_NOMEM);
+}
+
+/*
+** If parameter iDb is 1 (the temp db), or if connection handle db was not
+** opened with the SQLITE_OPEN_SHARED_SCHEMA flag, this function is a no-op.
+** Otherwise, it disconnects from the schema-pool associated with database
+** iDb, assuming it is connected.
+**
+** If parameter bNew is true, then Db.pSchema is set to point to a new, empty,
+** Schema object obtained from sqlite3_malloc(). Or, if bNew is false, then
+** Db.pSchema is set to NULL before returning.
+**
+** If the bNew parameter is true, then this function may allocate memory. 
+** If the allocation attempt fails, then SQLITE_NOMEM is returned and the
+** schema-pool is not disconnected from. Or, if no OOM error occurs, 
+** SQLITE_OK is returned.
+*/
+int sqlite3SchemaDisconnect(sqlite3 *db, int iDb, int bNew){
+  int rc = SQLITE_OK;
+  if( IsSharedSchema(db) ){
+    Db *pDb = &db->aDb[iDb];
+    SchemaPool *pSPool = pDb->pSPool;
+    assert_schema_state_ok(db);
+    assert( pDb->pSchema );
+
+    if( pSPool==0 ){
+      assert( pDb->pVTable==0 );
+      assert( bNew==0 );
+      schemaDelete(pDb->pSchema);
+      pDb->pSchema = 0;
+    }else{
+      VTable *p;
+      VTable *pNext;
+      for(p=pDb->pVTable; p; p=pNext){
+        pNext = p->pNext;
+        sqlite3VtabUnlock(p);
+      }
+      pDb->pVTable = 0;
+      sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+      if( DbHasProperty(db, iDb, DB_SchemaLoaded) ){
+        schemaRelease(db, pDb);
+      }
+      if( bNew ){
+        Schema *pNew = sqlite3SchemaGet(db, 0);
+        if( pNew==0 ){
+          rc = SQLITE_NOMEM;
+        }else{
+          pDb->pSchema = pNew;
+        }
+      }
+      if( rc==SQLITE_OK ){
+        assert( pSPool->nRef>=1 );
+        pDb->pSPool = 0;
+        pSPool->nRef--;
+        if( pSPool->nRef<=0 ){
+          SchemaPool **pp;
+          while( pSPool->pSchema ){
+            Schema *pNext = pSPool->pSchema->pNext;
+            schemaDelete(pSPool->pSchema);
+            pSPool->pSchema = pNext;
+          }
+          for(pp=&schemaPoolList; (*pp)!=pSPool; pp=&((*pp)->pNext));
+          *pp = pSPool->pNext;
+          sqlite3_free(pSPool);
+        }
+      }
+      sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+    }
+  }
+  return rc;
+}
+
+/*
+** Extract and return a pointer to a schema object from the SchemaPool passed
+** as the only argument, if one is available. If one is not available, return
+** NULL.
+*/
+Schema *sqlite3SchemaExtract(SchemaPool *pSPool){
+  Schema *pRet = 0;
+  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+  if( pSPool->pSchema ){
+    pRet = pSPool->pSchema;
+    pSPool->pSchema = pRet->pNext;
+    pRet->pNext = 0;
+  }
+  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+  return pRet;
+}
+
+/*
+** Return all sharable schemas held by database handle db back to their
+** respective schema-pools. Db.pSchema variables are left pointing to
+** the static, empty, Schema object owned by each schema-pool.
+*/
+void sqlite3SchemaReleaseAll(sqlite3 *db){
+  int i;
+  assert_schema_state_ok(db);
+  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+  for(i=0; i<db->nDb; i++){
+    if( i!=1 ){
+      Db *pDb = &db->aDb[i];
+      if( pDb->pSPool && DbHasProperty(db,i,DB_SchemaLoaded) ){
+        schemaRelease(db, pDb);
+      }
+    }
+  }
+  db->mDbFlags &= ~DBFLAG_FreeSchema;
+  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+}
+
+/*
+** Release any sharable schema held by connection iDb of database handle
+** db. Db.pSchema is left pointing to the static, empty, Schema object
+** owned by the schema-pool.
+*/
+void sqlite3SchemaRelease(sqlite3 *db, int iDb){
+  Db *pDb = &db->aDb[iDb];
+  assert( iDb!=1 );
+  assert_schema_state_ok(db);
+  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+  schemaRelease(db, pDb);
+  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
+}
+
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+
+/*
+** In most cases, this function finds and returns the schema associated 
+** with BTree handle pBt, creating a new one if necessary. However, if
+** the database handle was opened with the SQLITE_OPEN_SHARED_SCHEMA flag
+** specified, a new, empty, Schema object in memory obtained by 
+** sqlite3_malloc() is always returned.
 */
 Schema *sqlite3SchemaGet(sqlite3 *db, Btree *pBt){
-  Schema * p;
-  if( pBt ){
-    p = (Schema *)sqlite3BtreeSchema(pBt, sizeof(Schema), sqlite3SchemaClear);
+  Schema *p;
+  if( pBt && IsSharedSchema(db)==0 ){
+    p = (Schema*)sqlite3BtreeSchema(pBt, sizeof(Schema), sqlite3SchemaClear);
  }else{
-    p = (Schema *)sqlite3DbMallocZero(0, sizeof(Schema));
+    p = (Schema*)sqlite3DbMallocZero(0, sizeof(Schema));
  }
  if( !p ){
    sqlite3OomFault(db);
@@ -298,6 +298,9 @@ static const char * const sqlite3azCompileOpt[] = {
 #if SQLITE_ENABLE_SESSION
  "ENABLE_SESSION",
 #endif
+#if SQLITE_ENABLE_SHARED_SCHEMA
+  "ENABLE_SHARED_SCHEMA",
+#endif
 #if SQLITE_ENABLE_SNAPSHOT
  "ENABLE_SNAPSHOT",
 #endif
@@ -1413,9 +1413,9 @@ void sqlite3FkDelete(sqlite3 *db, Table *pTab){
  FKey *pFKey;                    /* Iterator variable */
  FKey *pNext;                    /* Copy of pFKey->pNextFrom */

-  assert( db==0 || IsVirtual(pTab)
-         || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );
  for(pFKey=pTab->pFKey; pFKey; pFKey=pNext){
+    assert( db==0 || IsVirtual(pTab)
+         || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );

    /* Remove the FK from the fkeyHash hash table. */
    if( !db || db->pnBytesFreed==0 ){
@@ -1159,6 +1159,17 @@ static void disconnectAllVtab(sqlite3 *db){
        if( IsVirtual(pTab) ) sqlite3VtabDisconnect(db, pTab);
      }
    }
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+    if( IsSharedSchema(db) && i!=1 ){
+      VTable *pVTable;
+      VTable *pNext;
+      for(pVTable=db->aDb[i].pVTable; pVTable; pVTable=pNext){
+        pNext = pVTable->pNext;
+        sqlite3VtabUnlock(pVTable);
+      }
+      db->aDb[i].pVTable = 0;
+    }
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
  }
  for(p=sqliteHashFirst(&db->aModule); p; p=sqliteHashNext(p)){
    Module *pMod = (Module *)sqliteHashData(p);
@@ -1327,6 +1338,7 @@ void sqlite3LeaveMutexAndCloseZombie(sqlite3 *db){
      sqlite3BtreeClose(pDb->pBt);
      pDb->pBt = 0;
      if( j!=1 ){
+        sqlite3SchemaDisconnect(db, j, 0);
        pDb->pSchema = 0;
      }
    }
@@ -3679,7 +3691,7 @@ int sqlite3_table_column_metadata(
  int *pPrimaryKey,           /* OUTPUT: True if column part of PK */
  int *pAutoinc               /* OUTPUT: True if column is auto-increment */
 ){
-  int rc;
+  int rc = SQLITE_OK;
  char *zErrMsg = 0;
  Table *pTab = 0;
  Column *pCol = 0;
@@ -3689,7 +3701,7 @@ int sqlite3_table_column_metadata(
  int notnull = 0;
  int primarykey = 0;
  int autoinc = 0;
-
+  int bUnlock;

 #ifdef SQLITE_ENABLE_API_ARMOR
  if( !sqlite3SafetyCheckOk(db) || zTableName==0 ){
@@ -3699,14 +3711,29 @@ int sqlite3_table_column_metadata(

  /* Ensure the database schema has been loaded */
  sqlite3_mutex_enter(db->mutex);
+  bUnlock = sqlite3LockReusableSchema(db);
  sqlite3BtreeEnterAll(db);
-  rc = sqlite3Init(db, &zErrMsg);
-  if( SQLITE_OK!=rc ){
-    goto error_out;
+  if( IsSharedSchema(db)==0 ){
+    rc = sqlite3Init(db, &zErrMsg);
  }

  /* Locate the table in question */
-  pTab = sqlite3FindTable(db, zTableName, zDbName);
+  if( rc==SQLITE_OK ){
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+    Parse sParse;                   /* Fake Parse object for FindTable */
+    Parse *pSaved = db->pParse;
+    memset(&sParse, 0, sizeof(sParse));
+    db->pParse = &sParse;
+#endif
+    pTab = sqlite3FindTable(db, zTableName, zDbName);
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+    sqlite3_free(sParse.zErrMsg);
+    rc = sParse.rc;
+    db->pParse = pSaved;
+#endif
+  }
+  if( SQLITE_OK!=rc ) goto error_out;
+
  if( !pTab || pTab->pSelect ){
    pTab = 0;
    goto error_out;
@@ -3779,6 +3806,7 @@ error_out:
  sqlite3ErrorWithMsg(db, rc, (zErrMsg?"%s":0), zErrMsg);
  sqlite3DbFree(db, zErrMsg);
  rc = sqlite3ApiExit(db, rc);
+  sqlite3UnlockReusableSchema(db, bUnlock);
  sqlite3_mutex_leave(db->mutex);
  return rc;
 }
@@ -471,7 +471,13 @@ void sqlite3Pragma(

  /* Make sure the database schema is loaded if the pragma requires that */
  if( (pPragma->mPragFlg & PragFlg_NeedSchema)!=0 ){
-    if( sqlite3ReadSchema(pParse) ) goto pragma_out;
+    if( IsSharedSchema(db) && (zDb || (pPragma->mPragFlg & PragFlg_OneSchema)) ){
+      assert( iDb>=0 && iDb<db->nDb );
+      pParse->rc = sqlite3SchemaLoad(db, iDb, 0, &pParse->zErrMsg);
+      if( pParse->rc ) goto pragma_out;
+    }else{
+      if( sqlite3ReadSchema(pParse) ) goto pragma_out;
+    }
  }

  /* Register the result column names for pragmas that return results */
@@ -1905,9 +1911,10 @@ void sqlite3Pragma(
  ** applications for any purpose.
  */
  case PragTyp_HEADER_VALUE: {
-    int iCookie = pPragma->iArg;  /* Which cookie to read or write */
+    int iCookie;                  /* Which cookie to read or write */
+    iCookie = pPragma->iArg & PRAGMA_HEADER_VALUE_MASK;     
    sqlite3VdbeUsesBtree(v, iDb);
-    if( zRight && (pPragma->mPragFlg & PragFlg_ReadOnly)==0 ){
+    if( zRight && (pPragma->iArg & PRAGMA_HEADER_VALUE_READONLY)==0 ){
      /* Write the specified cookie value */
      static const VdbeOpList setCookie[] = {
        { OP_Transaction,    0,  1,  0},    /* 0 */
@@ -55,12 +55,19 @@
 #define PragFlg_NeedSchema 0x01 /* Force schema load before running */
 #define PragFlg_NoColumns  0x02 /* OP_ResultRow called with zero columns */
 #define PragFlg_NoColumns1 0x04 /* zero columns if RHS argument is present */
-#define PragFlg_ReadOnly   0x08 /* Read-only HEADER_VALUE */
+#define PragFlg_OneSchema  0x08 /* Only a single schema required */
 #define PragFlg_Result0    0x10 /* Acts as query when no argument */
 #define PragFlg_Result1    0x20 /* Acts as query when has one argument */
 #define PragFlg_SchemaOpt  0x40 /* Schema restricts name search if present */
 #define PragFlg_SchemaReq  0x80 /* Schema required - "main" is default */

+/* For PragTyp_HEADER_VALUE pragmas the Pragma.iArg value is set
+** to the index of the header field to access (always 10 or less).
+** Ored with HEADER_VALUE_READONLY if the field is read only. */
+#define PRAGMA_HEADER_VALUE_READONLY 0x0100
+#define PRAGMA_HEADER_VALUE_MASK 0x00FF
+
+
 /* Names of columns for pragmas that return multi-column result
 ** or that return single-column results where the name of the
 ** result column is different from the name of the pragma
@@ -155,7 +162,7 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_AUTOVACUUM)
 {/* zName:     */ "auto_vacuum",
  /* ePragTyp:  */ PragTyp_AUTO_VACUUM,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1|PragFlg_OneSchema,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ 0 },
 #endif
@@ -176,7 +183,7 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_PAGER_PRAGMAS)
 {/* zName:     */ "cache_size",
  /* ePragTyp:  */ PragTyp_CACHE_SIZE,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1|PragFlg_OneSchema,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ 0 },
 #endif
@@ -237,21 +244,21 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)
 {/* zName:     */ "data_version",
  /* ePragTyp:  */ PragTyp_HEADER_VALUE,
-  /* ePragFlg:  */ PragFlg_ReadOnly|PragFlg_Result0,
+  /* ePragFlg:  */ PragFlg_Result0,
  /* ColNames:  */ 0, 0,
-  /* iArg:      */ BTREE_DATA_VERSION },
+  /* iArg:      */ BTREE_DATA_VERSION|PRAGMA_HEADER_VALUE_READONLY },
 #endif
 #if !defined(SQLITE_OMIT_SCHEMA_PRAGMAS)
 {/* zName:     */ "database_list",
  /* ePragTyp:  */ PragTyp_DATABASE_LIST,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_OneSchema,
  /* ColNames:  */ 41, 3,
  /* iArg:      */ 0 },
 #endif
 #if !defined(SQLITE_OMIT_PAGER_PRAGMAS) && !defined(SQLITE_OMIT_DEPRECATED)
 {/* zName:     */ "default_cache_size",
  /* ePragTyp:  */ PragTyp_DEFAULT_CACHE_SIZE,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1|PragFlg_OneSchema,
  /* ColNames:  */ 49, 1,
  /* iArg:      */ 0 },
 #endif
@@ -288,7 +295,7 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_FOREIGN_KEY)
 {/* zName:     */ "foreign_key_list",
  /* ePragTyp:  */ PragTyp_FOREIGN_KEY_LIST,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result1|PragFlg_SchemaOpt,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result1|PragFlg_SchemaOpt|PragFlg_OneSchema,
  /* ColNames:  */ 0, 8,
  /* iArg:      */ 0 },
 #endif
@@ -304,9 +311,9 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)
 {/* zName:     */ "freelist_count",
  /* ePragTyp:  */ PragTyp_HEADER_VALUE,
-  /* ePragFlg:  */ PragFlg_ReadOnly|PragFlg_Result0,
+  /* ePragFlg:  */ PragFlg_Result0,
  /* ColNames:  */ 0, 0,
-  /* iArg:      */ BTREE_FREE_PAGE_COUNT },
+  /* iArg:      */ BTREE_FREE_PAGE_COUNT|PRAGMA_HEADER_VALUE_READONLY },
 #endif
 #if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
 {/* zName:     */ "full_column_names",
@@ -346,7 +353,7 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_AUTOVACUUM)
 {/* zName:     */ "incremental_vacuum",
  /* ePragTyp:  */ PragTyp_INCREMENTAL_VACUUM,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_NoColumns,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_NoColumns|PragFlg_OneSchema,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ 0 },
 #endif
@@ -377,7 +384,7 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_PAGER_PRAGMAS)
 {/* zName:     */ "journal_mode",
  /* ePragTyp:  */ PragTyp_JOURNAL_MODE,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_OneSchema,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ 0 },
 {/* zName:     */ "journal_size_limit",
@@ -415,7 +422,7 @@ static const PragmaName aPragmaName[] = {
  /* iArg:      */ 0 },
 {/* zName:     */ "max_page_count",
  /* ePragTyp:  */ PragTyp_PAGE_COUNT,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_OneSchema,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ 0 },
 {/* zName:     */ "mmap_size",
@@ -443,7 +450,7 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_PAGER_PRAGMAS)
 {/* zName:     */ "page_count",
  /* ePragTyp:  */ PragTyp_PAGE_COUNT,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_OneSchema,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ 0 },
 {/* zName:     */ "page_size",
@@ -542,14 +549,14 @@ static const PragmaName aPragmaName[] = {
 #if !defined(SQLITE_OMIT_SCHEMA_PRAGMAS) && defined(SQLITE_DEBUG)
 {/* zName:     */ "stats",
  /* ePragTyp:  */ PragTyp_STATS,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_OneSchema,
  /* ColNames:  */ 27, 5,
  /* iArg:      */ 0 },
 #endif
 #if !defined(SQLITE_OMIT_PAGER_PRAGMAS)
 {/* zName:     */ "synchronous",
  /* ePragTyp:  */ PragTyp_SYNCHRONOUS,
-  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1|PragFlg_OneSchema,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ 0 },
 #endif
@@ -633,7 +640,7 @@ static const PragmaName aPragmaName[] = {
  /* iArg:      */ 0 },
 {/* zName:     */ "wal_checkpoint",
  /* ePragTyp:  */ PragTyp_WAL_CHECKPOINT,
-  /* ePragFlg:  */ PragFlg_NeedSchema,
+  /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_OneSchema,
  /* ColNames:  */ 44, 3,
  /* iArg:      */ 0 },
 #endif
@@ -34,6 +34,11 @@ static void corruptSchema(
    pData->rc = SQLITE_ERROR;
  }else if( db->flags & SQLITE_WriteSchema ){
    pData->rc = SQLITE_CORRUPT_BKPT;
+  }else if( IsSharedSchema(db) 
+         && 0==sqlite3StrNICmp(zExtra, "malformed database schema", 17)
+  ){
+    pData->rc = SQLITE_CORRUPT_BKPT;
+    *pData->pzErrMsg = sqlite3DbStrDup(db, zExtra);
  }else{
    char *z;
    if( zObj==0 ) zObj = "?";
@@ -44,6 +49,28 @@ static void corruptSchema(
  }
 }

+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+/*
+** Update the Schema.cksum checksum to account for the database object
+** specified by the three arguments following the first.
+*/
+static void schemaUpdateChecksum(
+  InitData *pData,                /* Schema parse context */
+  const char *zName,              /* Name of new database object */
+  const char *zRoot,              /* Root page of new database object */
+  const char *zSql                /* SQL used to create new database object */
+){
+  int i;
+  u64 cksum = pData->cksum;
+  if( zName ){
+    for(i=0; zName[i]; i++) cksum += (cksum<<3) + zName[i];
+  }
+  if( zRoot ) for(i=0; zRoot[i]; i++) cksum += (cksum<<3) + zRoot[i];
+  if( zSql ) for(i=0; zSql[i]; i++) cksum += (cksum<<3) + zSql[i];
+  pData->cksum = cksum;
+}
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+
 /*
 ** Check to see if any sibling index (another index on the same table)
 ** of pIndex has the same root page number, and if it does, return true.
@@ -67,6 +94,15 @@ static int sqlite3Prepare(
  sqlite3_stmt **ppStmt,    /* OUT: A pointer to the prepared statement */
  const char **pzTail       /* OUT: End of parsed string */
 );
+static int sqlite3LockAndPrepare(
+  sqlite3 *db,              /* Database handle. */
+  const char *zSql,         /* UTF-8 encoded SQL statement. */
+  int nBytes,               /* Length of zSql in bytes. */
+  u32 prepFlags,            /* Zero or more SQLITE_PREPARE_* flags */
+  Vdbe *pReprepare,         /* VM being reprepared */
+  sqlite3_stmt **ppStmt,    /* OUT: A pointer to the prepared statement */
+  const char **pzTail       /* OUT: End of parsed string */
+);


 /*
@@ -125,7 +161,11 @@ int sqlite3InitCallback(void *pInit, int argc, char **argv, char **NotUsed){
    db->init.orphanTrigger = 0;
    db->init.azInit = argv;
    pStmt = 0;
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+    TESTONLY(rcp = ) sqlite3LockAndPrepare(db, argv[4], -1, 0, 0, &pStmt, 0);
+#else
    TESTONLY(rcp = ) sqlite3Prepare(db, argv[4], -1, 0, 0, &pStmt, 0);
+#endif
    rc = db->errCode;
    assert( (rc&0xFF)==(rcp&0xFF) );
    db->init.iDb = saved_iDb;
@@ -137,7 +177,12 @@ int sqlite3InitCallback(void *pInit, int argc, char **argv, char **NotUsed){
        if( rc > pData->rc ) pData->rc = rc;
        if( rc==SQLITE_NOMEM ){
          sqlite3OomFault(db);
-        }else if( rc!=SQLITE_INTERRUPT && (rc&0xFF)!=SQLITE_LOCKED ){
+        }else if( rc!=SQLITE_INTERRUPT 
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+               && (rc&0xFF)!=SQLITE_LOCKED 
+               && (rc&0xFF)!=SQLITE_IOERR
+#endif
+        ){
          corruptSchema(pData, argv[1], sqlite3_errmsg(db));
        }
      }
@@ -167,6 +212,12 @@ int sqlite3InitCallback(void *pInit, int argc, char **argv, char **NotUsed){
      }
    }
  }
+
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  if( IsSharedSchema(db) && iDb!=1 ){
+    schemaUpdateChecksum(pData, argv[0], argv[1], argv[2]);
+  }
+#endif
  return 0;
 }

@@ -194,10 +245,28 @@ int sqlite3InitOne(sqlite3 *db, int iDb, char **pzErrMsg, u32 mFlags){

  assert( (db->mDbFlags & DBFLAG_SchemaKnownOk)==0 );
  assert( iDb>=0 && iDb<db->nDb );
-  assert( db->aDb[iDb].pSchema );
+  assert( db->aDb[iDb].pSchema || (IsSharedSchema(db) && iDb!=1) );
  assert( sqlite3_mutex_held(db->mutex) );
  assert( iDb==1 || sqlite3BtreeHoldsMutex(db->aDb[iDb].pBt) );

+  pDb = &db->aDb[iDb];
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  assert( pDb->pSPool==0 || IsSharedSchema(db) );
+  if( pDb->pSPool ){
+    /* See if there is a free schema object in the schema-pool. If not,
+    ** disconnect from said schema pool and continue. This function will
+    ** connect to a (possibly different) schema-pool before returning. */
+    Schema *pNew = sqlite3SchemaExtract(pDb->pSPool);
+    if( pNew ){
+      pDb->pSchema = pNew;
+      return SQLITE_OK;
+    }
+    rc = sqlite3SchemaDisconnect(db, iDb, 1);
+    if( rc!=SQLITE_OK ) goto error_out;
+    assert( pDb->pSchema && pDb->pSPool==0 );
+  }
+#endif
+
  db->init.busy = 1;

  /* Construct the in-memory representation schema tables (sqlite_schema or
@@ -218,6 +287,7 @@ int sqlite3InitOne(sqlite3 *db, int iDb, char **pzErrMsg, u32 mFlags){
  initData.pzErrMsg = pzErrMsg;
  initData.mInitFlags = mFlags;
  initData.nInitRow = 0;
+  initData.cksum = 0;
  initData.mxPage = 0;
  sqlite3InitCallback(&initData, 5, (char **)azArg, 0);
  db->mDbFlags &= mask;
@@ -228,7 +298,6 @@ int sqlite3InitOne(sqlite3 *db, int iDb, char **pzErrMsg, u32 mFlags){

  /* Create a cursor to hold the database open
  */
-  pDb = &db->aDb[iDb];
  if( pDb->pBt==0 ){
    assert( iDb==1 );
    DbSetProperty(db, 1, DB_SchemaLoaded);
@@ -383,6 +452,10 @@ int sqlite3InitOne(sqlite3 *db, int iDb, char **pzErrMsg, u32 mFlags){
    rc = SQLITE_OK;
  }

+  if( rc==SQLITE_OK && iDb!=1 && IsSharedSchema(db) ){
+    rc = sqlite3SchemaConnect(db, iDb, initData.cksum);
+  }
+
  /* Jump here for an error that occurs after successfully allocating
  ** curMain and calling sqlite3BtreeEnter(). For an error that occurs
  ** before that point, jump to error_out.
@@ -404,6 +477,35 @@ error_out:
  return rc;
 }

+
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+/*
+** If this is a SHARED_SCHEMA connection and the DBFLAG_SchemaInUse flag
+** is not currently set, set it and return non-zero. Otherwise, return 0.
+*/
+int sqlite3LockReusableSchema(sqlite3 *db){
+  if( IsSharedSchema(db) && (db->mDbFlags & DBFLAG_SchemaInuse)==0 ){
+    db->mDbFlags |= DBFLAG_SchemaInuse;
+    return 1;
+  }
+  return 0;
+}
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+/*
+** This function is a no-op for non-SHARED_SCHEMA connections, or if bRelease
+** is zero. Otherwise, clear the DBFLAG_SchemaInuse flag and release all
+** schema references currently held.
+*/
+void sqlite3UnlockReusableSchema(sqlite3 *db, int bRelease){
+  if( bRelease ){
+    db->mDbFlags &= ~DBFLAG_SchemaInuse;
+    sqlite3SchemaReleaseAll(db);
+  }
+}
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+
 /*
 ** Initialize all database files - the main database file, the file
 ** used to store temporary tables, and any additional database files
@@ -414,8 +516,12 @@ error_out:
 ** bit is set in the flags field of the Db structure. 
 */
 int sqlite3Init(sqlite3 *db, char **pzErrMsg){
-  int i, rc;
+  int rc = SQLITE_OK;
+  int bReleaseSchema;
+  int i;
  int commit_internal = !(db->mDbFlags&DBFLAG_SchemaChange);
+
+  bReleaseSchema = sqlite3LockReusableSchema(db);
  
  assert( sqlite3_mutex_held(db->mutex) );
  assert( sqlite3BtreeHoldsMutex(db->aDb[0].pBt) );
@@ -425,20 +531,19 @@ int sqlite3Init(sqlite3 *db, char **pzErrMsg){
  /* Do the main schema first */
  if( !DbHasProperty(db, 0, DB_SchemaLoaded) ){
    rc = sqlite3InitOne(db, 0, pzErrMsg, 0);
-    if( rc ) return rc;
  }
  /* All other schemas after the main schema. The "temp" schema must be last */
-  for(i=db->nDb-1; i>0; i--){
+  for(i=db->nDb-1; rc==SQLITE_OK && i>0; i--){
    assert( i==1 || sqlite3BtreeHoldsMutex(db->aDb[i].pBt) );
    if( !DbHasProperty(db, i, DB_SchemaLoaded) ){
      rc = sqlite3InitOne(db, i, pzErrMsg, 0);
-      if( rc ) return rc;
    }
  }
-  if( commit_internal ){
+  if( rc==SQLITE_OK && commit_internal ){
    sqlite3CommitInternalChanges(db);
  }
-  return SQLITE_OK;
+  sqlite3UnlockReusableSchema(db, bReleaseSchema);
+  return rc;
 }

 /*
@@ -450,11 +555,12 @@ int sqlite3ReadSchema(Parse *pParse){
  sqlite3 *db = pParse->db;
  assert( sqlite3_mutex_held(db->mutex) );
  if( !db->init.busy ){
+    db->mDbFlags |= DBFLAG_FreeSchema;      /* For sharable-schema mode */
    rc = sqlite3Init(db, &pParse->zErrMsg);
    if( rc!=SQLITE_OK ){
      pParse->rc = rc;
      pParse->nErr++;
-    }else if( db->noSharedCache ){
+    }else if( db->noSharedCache && !IsSharedSchema(db) ){
      db->mDbFlags |= DBFLAG_SchemaKnownOk;
    }
  }
@@ -480,6 +586,10 @@ static void schemaIsValid(Parse *pParse){
    Btree *pBt = db->aDb[iDb].pBt;     /* Btree database to read cookie from */
    if( pBt==0 ) continue;

+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+    if( IsSharedSchema(db) && iDb!=1 && db->aDb[iDb].pSPool==0 ) continue;
+#endif
+
    /* If there is not already a read-only (or read-write) transaction opened
    ** on the b-tree database, open one now. If a transaction is opened, it 
    ** will be closed immediately after reading the meta-value. */
@@ -725,6 +835,7 @@ static int sqlite3LockAndPrepare(
 ){
  int rc;
  int cnt = 0;
+  int bReleaseSchema = 0;

 #ifdef SQLITE_ENABLE_API_ARMOR
  if( ppStmt==0 ) return SQLITE_MISUSE_BKPT;
@@ -734,6 +845,7 @@ static int sqlite3LockAndPrepare(
    return SQLITE_MISUSE_BKPT;
  }
  sqlite3_mutex_enter(db->mutex);
+  bReleaseSchema = sqlite3LockReusableSchema(db);
  sqlite3BtreeEnterAll(db);
  do{
    /* Make multiple attempts to compile the SQL, until it either succeeds
@@ -743,7 +855,11 @@ static int sqlite3LockAndPrepare(
    assert( rc==SQLITE_OK || *ppStmt==0 );
  }while( rc==SQLITE_ERROR_RETRY
       || (rc==SQLITE_SCHEMA && (sqlite3ResetOneSchema(db,-1), cnt++)==0) );
+
  sqlite3BtreeLeaveAll(db);
+
+  sqlite3UnlockReusableSchema(db, bReleaseSchema);
+
  rc = sqlite3ApiExit(db, rc);
  assert( (rc&db->errMask)==rc );
  db->busyHandler.nBusy = 0;
@@ -5615,7 +5615,9 @@ static void explainSimpleCount(
 static int havingToWhereExprCb(Walker *pWalker, Expr *pExpr){
  if( pExpr->op!=TK_AND ){
    Select *pS = pWalker->u.pSelect;
-    if( sqlite3ExprIsConstantOrGroupBy(pWalker->pParse, pExpr, pS->pGroupBy) ){
+    if( sqlite3ExprIsConstantOrGroupBy(pWalker->pParse, pExpr, pS->pGroupBy) 
+     && ExprAlwaysFalse(pExpr)==0
+    ){
      sqlite3 *db = pWalker->pParse->db;
      Expr *pNew = sqlite3Expr(db, TK_INTEGER, "1");
      if( pNew ){
@@ -1152,13 +1152,14 @@ struct ShellState {

 /* Allowed values for ShellState.openMode
 */
-#define SHELL_OPEN_UNSPEC      0      /* No open-mode specified */
-#define SHELL_OPEN_NORMAL      1      /* Normal database file */
-#define SHELL_OPEN_APPENDVFS   2      /* Use appendvfs */
-#define SHELL_OPEN_ZIPFILE     3      /* Use the zipfile virtual table */
-#define SHELL_OPEN_READONLY    4      /* Open a normal database read-only */
-#define SHELL_OPEN_DESERIALIZE 5      /* Open using sqlite3_deserialize() */
-#define SHELL_OPEN_HEXDB       6      /* Use "dbtotxt" output as data source */
+#define SHELL_OPEN_UNSPEC       0     /* No open-mode specified */
+#define SHELL_OPEN_NORMAL       1     /* Normal database file */
+#define SHELL_OPEN_APPENDVFS    2     /* Use appendvfs */
+#define SHELL_OPEN_ZIPFILE      3     /* Use the zipfile virtual table */
+#define SHELL_OPEN_READONLY     4     /* Open a normal database read-only */
+#define SHELL_OPEN_DESERIALIZE  5     /* Open using sqlite3_deserialize() */
+#define SHELL_OPEN_HEXDB        6     /* Use "dbtotxt" output as data source */
+#define SHELL_OPEN_SHAREDSCHEMA 7     /* Open for schema reuse */

 /* Allowed values for ShellState.eTraceType
 */
@@ -4043,6 +4044,12 @@ static const char *(azHelp[]) = {
  "      --sha3-384            Use the sha3-384 algorithm",
  "      --sha3-512            Use the sha3-512 algorithm",
  "    Any other argument is a LIKE pattern for tables to hash",
+#if !defined(SQLITE_OMIT_VIRTUALTABLE) && defined(SQLITE_ENABLE_DBPAGE_VTAB)
+  ".shared-schema CMD DB1 DB2 ...",
+  "    Commands:",
+  "       check                Determine if DB1, DB2, etc have identical schemas",
+  "       fix                  Attempt to make DB1, DB2, etc compatible",
+#endif
 #ifndef SQLITE_NOHAVE_SYSTEM
  ".shell CMD ARGS...       Run CMD ARGS... in a system shell",
 #endif
@@ -4575,6 +4582,11 @@ static void open_db(ShellState *p, int openFlags){
            SQLITE_OPEN_READONLY|p->openFlags, 0);
        break;
      }
+      case SHELL_OPEN_SHAREDSCHEMA: {
+        sqlite3_open_v2(p->zDbFilename, &p->db,
+          SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_SHARED_SCHEMA,0);
+        break;
+      }
      case SHELL_OPEN_UNSPEC:
      case SHELL_OPEN_NORMAL: {
        sqlite3_open_v2(p->zDbFilename, &p->db,
@@ -6768,6 +6780,237 @@ static char *shellMPrintf(int *pRc, const char *zFmt, ...){
  }
  return z;
 }
+static int sharedSchemaFix(ShellState *pState, const char *zDb, int eFix){
+  int rc = SQLITE_OK;
+  i64 iLast = 0;
+  int iCookie = 0;
+  int iAutoVacuum = 0;
+  sqlite3_stmt *pStmt = 0;
+
+  shellExecPrintf(pState->db, &rc, "ATTACH '%q' AS _shared_schema_tmp", zDb);
+  shellExecPrintf(pState->db, &rc, "PRAGMA writable_schema = 1");
+  shellExecPrintf(pState->db, &rc, "BEGIN");
+  shellPreparePrintf(pState->db, &rc, &pStmt, 
+      "SELECT max(rowid) FROM _shared_schema_tmp.sqlite_master"
+  );
+  sqlite3_step(pStmt);
+  iLast = sqlite3_column_int64(pStmt, 0);
+  shellFinalize(&rc, pStmt);
+  shellPreparePrintf(pState->db, &rc, &pStmt,
+      "INSERT INTO _shared_schema_tmp.sqlite_master SELECT "
+      "  type, name, tbl_name, ("
+      "    SELECT rootpage FROM _shared_schema_tmp.sqlite_master WHERE "
+      "      type IS o.type AND name IS o.name AND rowid<=?"
+      "  ), sql FROM main.sqlite_master AS o"
+  );
+  sqlite3_bind_int64(pStmt, 1, iLast);
+  sqlite3_step(pStmt);
+  shellFinalize(&rc, pStmt);
+
+  shellExecPrintf(pState->db, &rc,
+      "DELETE FROM _shared_schema_tmp.sqlite_master WHERE rowid<=%lld",
+      iLast
+  );
+  shellExecPrintf(pState->db, &rc, "COMMIT");
+  sqlite3_exec(pState->db, "PRAGMA writable_schema = 0", 0, 0, 0);
+
+  /* Copy the auto-vacuum setting from main to the target db */
+  shellPreparePrintf(pState->db, &rc, &pStmt, "PRAGMA main.auto_vacuum");
+  sqlite3_step(pStmt);
+  iAutoVacuum = sqlite3_column_int(pStmt, 0);
+  shellFinalize(&rc, pStmt);
+  shellExecPrintf(pState->db, &rc, 
+      "PRAGMA _shared_schema_tmp.auto_vacuum = %d", iAutoVacuum
+  );
+
+  /* Vacuum the db in order to standardize the rootpage numbers. */
+  shellExecPrintf(pState->db, &rc, "VACUUM _shared_schema_tmp");
+
+  /* Set the schema-cookie value to the same as database "main" */
+  shellPreparePrintf(pState->db, &rc, &pStmt, "PRAGMA main.schema_version");
+  sqlite3_step(pStmt);
+  iCookie = sqlite3_column_int(pStmt, 0);
+  shellFinalize(&rc, pStmt);
+  shellExecPrintf(pState->db, &rc, 
+      "PRAGMA _shared_schema_tmp.schema_version = %d", iCookie
+  );
+
+  sqlite3_exec(pState->db, "DETACH _shared_schema_tmp", 0, 0, 0);
+  return rc;
+}
+
+static int sharedSchemaCheck(ShellState *pState, const char *zDb, int *peFix){
+  int rc = SQLITE_OK;
+  int bFailed = 0;
+  sqlite3_stmt *pStmt = 0;
+
+  if( peFix ) *peFix = 0;
+  shellExecPrintf(pState->db, &rc, "ATTACH '%q' AS _shared_schema_tmp", zDb);
+
+  /* Check if this database has the same set of objects as the current db */
+  shellPreparePrintf(pState->db, &rc, &pStmt, 
+    "SELECT type, name FROM _shared_schema_tmp.sqlite_master AS o "
+    "WHERE NOT EXISTS ("
+    "  SELECT 1 FROM main.sqlite_master "
+    "    WHERE name IS o.name AND type IS o.type"
+    ")"
+    " UNION ALL "
+    "SELECT type, name FROM main.sqlite_master AS o "
+    "WHERE NOT EXISTS ("
+    "  SELECT 1 FROM _shared_schema_tmp.sqlite_master "
+    "    WHERE name IS o.name AND type IS o.type"
+    ")"
+  );
+  if( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+    utf8_printf(pState->out, "%s is NOT compatible (objects)\n", zDb);
+    bFailed = 1;
+  }
+  shellFinalize(&rc, pStmt);
+
+  /* Check if this database has the same set of SQL statements as the 
+  ** current db. */
+  if( bFailed==0 ){
+    shellPreparePrintf(pState->db, &rc, &pStmt, 
+        "SELECT 1 FROM _shared_schema_tmp.sqlite_master AS o "
+        "WHERE sql IS NOT ("
+        "  SELECT sql FROM main.sqlite_master "
+        "    WHERE name IS o.name AND type IS o.type"
+        ")"
+    );
+    if( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+      utf8_printf(pState->out, "%s is NOT compatible (SQL)\n", zDb);
+      bFailed = 1;
+    }
+    shellFinalize(&rc, pStmt);
+  }
+
+  /* Check if this database has the same set of root pages as the current 
+  ** db. */
+  if( bFailed==0 ){
+    shellPreparePrintf(pState->db, &rc, &pStmt, 
+        "SELECT 1 FROM _shared_schema_tmp.sqlite_master AS o "
+        "WHERE rootpage IS NOT ("
+        "  SELECT rootpage FROM main.sqlite_master "
+        "    WHERE name IS o.name AND type IS o.type"
+        ")"
+    );
+    if( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+      if( peFix==0 ){
+        utf8_printf(pState->out, "%s is NOT compatible (root pages)\n", zDb);
+      }
+      bFailed = 1;
+      if( peFix ) *peFix = 1;
+    }
+    shellFinalize(&rc, pStmt);
+  }
+
+  if( bFailed==0 ){
+    shellPreparePrintf(pState->db, &rc, &pStmt, 
+        "SELECT 1 WHERE ("
+        "  SELECT group_concat(rootpage || '.' || name || '.' || sql, '.') "
+        "  FROM _shared_schema_tmp.sqlite_master"
+        ") IS NOT ("
+        "  SELECT group_concat(rootpage || '.' || name || '.' || sql, '.') "
+        "  FROM main.sqlite_master"
+        ")"
+    );
+    if( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+      if( peFix==0 ){
+        utf8_printf(pState->out, 
+            "%s is NOT compatible (order of sqlite_master rows)\n", zDb
+        );
+      }
+      bFailed = 1;
+      if( peFix ) *peFix = 2;
+    }
+    shellFinalize(&rc, pStmt);
+  }
+
+  if( bFailed==0 ){
+    int iMain = -1;
+    int iNew = +1;
+    shellPreparePrintf(pState->db, &rc, &pStmt, 
+        "PRAGMA main.schema_version"
+    );
+    if( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+      iMain = sqlite3_column_int(pStmt, 0);
+    }
+    shellFinalize(&rc, pStmt);
+    shellPreparePrintf(pState->db, &rc, &pStmt, 
+        "PRAGMA _shared_schema_tmp.schema_version"
+    );
+    if( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+      iNew = sqlite3_column_int(pStmt, 0);
+    }
+    shellFinalize(&rc, pStmt);
+    if( rc==SQLITE_OK && iMain!=iNew ){
+      if( peFix==0 ){
+        utf8_printf(pState->out, 
+            "%s is NOT compatible (schema cookie)\n", zDb
+        );
+      }
+      bFailed = 1;
+      if( peFix ) *peFix = 3;
+    }
+  }
+
+  if( rc==SQLITE_OK && bFailed==0 ){
+    utf8_printf(pState->out, "%s is compatible\n", zDb);
+  }
+
+  sqlite3_exec(pState->db, "DETACH _shared_schema_tmp", 0, 0, 0);
+  return rc;
+}
+
+/*
+** .shared-schema check|fix DB1 DB2...
+*/
+static int sharedSchemaDotCommand(
+  ShellState *pState,             /* Current shell tool state */
+  char **azArg,                   /* Array of arguments passed to dot command */
+  int nArg                        /* Number of entries in azArg[] */
+){
+  int rc = SQLITE_OK;
+  int bFix = 0;                   /* Fix databases if possible */
+  int n1;
+  int i;
+  if( nArg<3 ){
+    goto shared_schema_usage;
+  }
+
+  n1 = (int)strlen(azArg[1]);
+  if( n1>0 && n1<=3 && memcmp("fix", azArg[1], n1)==0 ){
+    bFix = 1;
+  }else if( n1==0 || n1>5 || memcmp("check", azArg[1], n1) ){
+    goto shared_schema_usage;
+  }
+
+  for(i=2; rc==SQLITE_OK && i<nArg; i++){
+    int eFix = 0;
+    rc = sharedSchemaCheck(pState, azArg[i], bFix ? &eFix : 0);
+    if( rc==SQLITE_OK && bFix && eFix ){
+      utf8_printf(pState->out, "Fixing %s... ", azArg[i]);
+      fflush(pState->out);
+      rc = sharedSchemaFix(pState, azArg[i], eFix);
+      if( rc==SQLITE_OK ){
+        rc = sharedSchemaCheck(pState, azArg[i], &eFix);
+        if( rc==SQLITE_OK && eFix ){
+          utf8_printf(pState->out, "VACUUMing main... ");
+          fflush(pState->out);
+          rc = sqlite3_exec(pState->db, "VACUUM main", 0, 0, 0);
+          if( rc==SQLITE_OK ){
+            rc = sharedSchemaCheck(pState, azArg[i], 0);
+          }
+        }
+      }
+    }
+  }
+
+  return rc;
+ shared_schema_usage:
+  raw_printf(stderr, "usage: .shared-schema check|fix DB1 DB2...\n");
+  return SQLITE_ERROR;
+}

 /*
 ** When running the ".recover" command, each output table, and the special
@@ -8693,6 +8936,8 @@ static int do_meta_command(char *zLine, ShellState *p){
        p->openMode = SHELL_OPEN_APPENDVFS;
      }else if( optionMatch(z, "readonly") ){
        p->openMode = SHELL_OPEN_READONLY;
+      }else if( optionMatch(z, "sharedschema") ){
+        p->openMode = SHELL_OPEN_SHAREDSCHEMA;
      }else if( optionMatch(z, "nofollow") ){
        p->openFlags |= SQLITE_OPEN_NOFOLLOW;
 #ifdef SQLITE_ENABLE_DESERIALIZE
@@ -9698,6 +9943,13 @@ static int do_meta_command(char *zLine, ShellState *p){
    sqlite3_free(zSql);
  }else

+#if !defined(SQLITE_OMIT_VIRTUALTABLE) && defined(SQLITE_ENABLE_DBPAGE_VTAB)
+  if( c=='s' && strncmp(azArg[0], "shared-schema", n)==0 ){
+    open_db(p, 0);
+    sharedSchemaDotCommand(p, azArg, nArg);
+  }else
+#endif
+
 #ifndef SQLITE_NOHAVE_SYSTEM
  if( c=='s'
   && (strncmp(azArg[0], "shell", n)==0 || strncmp(azArg[0],"system",n)==0)
@@ -11014,6 +11266,8 @@ int SQLITE_CDECL wmain(int argc, wchar_t **wargv){
 #endif
    }else if( strcmp(z,"-readonly")==0 ){
      data.openMode = SHELL_OPEN_READONLY;
+    }else if( strcmp(z,"-sharedschema")==0 ){
+      data.openMode = SHELL_OPEN_SHAREDSCHEMA;
    }else if( strcmp(z,"-nofollow")==0 ){
      data.openFlags = SQLITE_OPEN_NOFOLLOW;
 #if !defined(SQLITE_OMIT_VIRTUALTABLE) && defined(SQLITE_HAVE_ZLIB)
@@ -11131,6 +11385,8 @@ int SQLITE_CDECL wmain(int argc, wchar_t **wargv){
 #endif
    }else if( strcmp(z,"-readonly")==0 ){
      data.openMode = SHELL_OPEN_READONLY;
+    }else if( strcmp(z,"-sharedschema")==0 ){
+      data.openMode = SHELL_OPEN_SHAREDSCHEMA;
    }else if( strcmp(z,"-nofollow")==0 ){
      data.openFlags |= SQLITE_OPEN_NOFOLLOW;
    }else if( strcmp(z,"-ascii")==0 ){
@@ -574,10 +574,11 @@ int sqlite3_exec(
 #define SQLITE_OPEN_NOFOLLOW         0x01000000  /* Ok for sqlite3_open_v2() */

 /* Reserved:                         0x00F00000 */
+#define SQLITE_OPEN_SHARED_SCHEMA    0x01000000  /* Ok for sqlite3_open_v2() */
+
 /* Legacy compatibility: */
 #define SQLITE_OPEN_MASTER_JOURNAL   0x00004000  /* VFS only */

-
 /*
 ** CAPI3REF: Device Characteristics
 **
@@ -3697,7 +3698,7 @@ sqlite3_file *sqlite3_database_file_object(const char*);
 ** If the Y parameter to sqlite3_free_filename(Y) is anything other
 ** than a NULL pointer or a pointer previously acquired from
 ** sqlite3_create_filename(), then bad things such as heap
-** corruption or segfaults may occur. The value Y should be 
+** corruption or segfaults may occur. The value Y should not be 
 ** used again after sqlite3_free_filename(Y) has been called.  This means
 ** that if the [sqlite3_vfs.xOpen()] method of a VFS has been called using Y,
 ** then the corresponding [sqlite3_module.xClose() method should also be
@@ -1127,6 +1127,7 @@ typedef struct CollSeq CollSeq;
 typedef struct Column Column;
 typedef struct Db Db;
 typedef struct Schema Schema;
+typedef struct SchemaPool SchemaPool;
 typedef struct Expr Expr;
 typedef struct ExprList ExprList;
 typedef struct FKey FKey;
@@ -1260,6 +1261,10 @@ struct Db {
  u8 safety_level;     /* How aggressive at syncing data to disk */
  u8 bSyncSet;         /* True if "PRAGMA synchronous=N" has been run */
  Schema *pSchema;     /* Pointer to database schema (possibly shared) */
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  SchemaPool *pSPool;  /* For REUSE_SCHEMA mode */
+  VTable *pVTable;     /* List of all VTable objects (REUSE_SCHEMA mode only) */
+#endif
 };

 /*
@@ -1291,6 +1296,9 @@ struct Schema {
  u8 enc;              /* Text encoding used by this database */
  u16 schemaFlags;     /* Flags associated with this schema */
  int cache_size;      /* Number of pages to use in the cache */
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  Schema *pNext;       /* Next Schema object SchemaPool (REUSE_SCHEMA) */
+#endif
 };

 /*
@@ -1606,6 +1614,12 @@ struct sqlite3 {
 #endif
 };

+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+# define IsSharedSchema(db) (((db)->openFlags & SQLITE_OPEN_SHARED_SCHEMA)!=0)
+#else
+# define IsSharedSchema(db) 0
+#endif
+
 /*
 ** A macro to discover the encoding of a database.
 */
@@ -1686,6 +1700,9 @@ struct sqlite3 {
 #define DBFLAG_InternalFunc   0x0020  /* Allow use of internal functions */
 #define DBFLAG_EncodingFixed  0x0040  /* No longer possible to change enc. */

+#define DBFLAG_SchemaInuse    0x0080  /* Do not release sharable schemas */
+#define DBFLAG_FreeSchema     0x0100  /* Free extra shared schemas on release */
+
 /*
 ** Bits of the sqlite3.dbOptFlags field that are used by the
 ** sqlite3_test_control(SQLITE_TESTCTRL_OPTIMIZATIONS,...) interface to
@@ -2126,6 +2143,9 @@ struct VTable {
  u8 eVtabRisk;             /* Riskiness of allowing hacker access */
  int iSavepoint;           /* Depth of the SAVEPOINT stack */
  VTable *pNext;            /* Next in linked list (see above) */
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  char *zName;              /* Table name (REUSE_SCHEMA mode) */
+#endif
 };

 /* Allowed values for VTable.eVtabRisk
@@ -3376,7 +3396,6 @@ struct Parse {
  AutoincInfo *pAinc;  /* Information about AUTOINCREMENT counters */
  Parse *pToplevel;    /* Parse structure for main program (or NULL) */
  Table *pTriggerTab;  /* Table triggers are being coded for */
-  Parse *pParentParse; /* Parent parser if this parser is nested */
  AggInfo *pAggList;   /* List of all AggInfo objects */
  int addrCrTab;       /* Address of OP_CreateBtree opcode on CREATE TABLE */
  u32 nQueryLoop;      /* Est number of iterations of a query (10*log2(N)) */
@@ -3539,6 +3558,9 @@ struct Trigger {
  Schema *pTabSchema;     /* Schema containing the table */
  TriggerStep *step_list; /* Link list of trigger program steps             */
  Trigger *pNext;         /* Next trigger associated with the table */
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  char *zTabSchema;       /* Temp triggers in IsSharedSchema() dbs only */
+#endif
 };

 /*
@@ -3651,6 +3673,7 @@ typedef struct {
  int rc;             /* Result code stored here */
  u32 mInitFlags;     /* Flags controlling error messages */
  u32 nInitRow;       /* Number of rows processed */
+  u64 cksum;          /* Schema checksum for REUSE_SCHEMA mode */
  Pgno mxPage;        /* Maximum page number.  0 for no limit. */
 } InitData;

@@ -4659,6 +4682,29 @@ void sqlite3DefaultRowEst(Index*);
 void sqlite3RegisterLikeFunctions(sqlite3*, int);
 int sqlite3IsLikeFunction(sqlite3*,Expr*,int*,char*);
 void sqlite3SchemaClear(void *);
+void sqlite3SchemaClearOrDisconnect(sqlite3*, int);
+
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA 
+int sqlite3SchemaConnect(sqlite3*, int, u64);
+int sqlite3SchemaDisconnect(sqlite3 *, int, int);
+Schema *sqlite3SchemaExtract(SchemaPool*);
+int sqlite3SchemaLoad(sqlite3*, int, int*, char**);
+void sqlite3SchemaReleaseAll(sqlite3*);
+void sqlite3SchemaRelease(sqlite3*, int);
+void sqlite3SchemaAdjustUsed(sqlite3*, int, int, int*);
+void sqlite3SchemaWritable(Parse*, int);
+void sqlite3UnlockReusableSchema(sqlite3 *db, int bRelease);
+int sqlite3LockReusableSchema(sqlite3 *db);
+#else
+# define sqlite3SchemaWritable(x,y)
+# define sqlite3UnlockReusableSchema(x,y)
+# define sqlite3LockReusableSchema(x) 0
+# define sqlite3SchemaDisconnect(x,y,z) SQLITE_OK
+# define sqlite3SchemaLoad(w,x,y,z) SQLITE_OK
+# define sqlite3SchemaRelease(y,z)
+# define sqlite3SchemaConnect(x,y,z) SQLITE_OK
+#endif
+
 Schema *sqlite3SchemaGet(sqlite3 *, Btree *);
 int sqlite3SchemaToIndex(sqlite3 *db, Schema *);
 KeyInfo *sqlite3KeyInfoAlloc(sqlite3*,int,int);
@@ -288,11 +288,24 @@ int sqlite3_db_status(
    case SQLITE_DBSTATUS_SCHEMA_USED: {
      int i;                      /* Used to iterate through schemas */
      int nByte = 0;              /* Used to accumulate return value */
+      int bReleaseSchema;

      sqlite3BtreeEnterAll(db);
+      bReleaseSchema = sqlite3LockReusableSchema(db);
      db->pnBytesFreed = &nByte;
      for(i=0; i<db->nDb; i++){
-        Schema *pSchema = db->aDb[i].pSchema;
+        Schema *pSchema;
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+        int bUnload = 0;
+        int nUsed = nByte;
+        if( db->aDb[i].pSPool ){
+          char *zDummy = 0;
+          rc = sqlite3SchemaLoad(db, i, &bUnload, &zDummy);
+          sqlite3_free(zDummy);
+          if( rc ) break;
+        }
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+        pSchema = db->aDb[i].pSchema;
        if( ALWAYS(pSchema!=0) ){
          HashElem *p;

@@ -314,7 +327,14 @@ int sqlite3_db_status(
            sqlite3DeleteTable(db, (Table *)sqliteHashData(p));
          }
        }
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+        if( db->aDb[i].pSPool ){
+          if( bUnload ) sqlite3SchemaRelease(db, i);
+          sqlite3SchemaAdjustUsed(db, i, nUsed, &nByte);
+        }
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
      }
+      sqlite3UnlockReusableSchema(db, bReleaseSchema);
      db->pnBytesFreed = 0;
      sqlite3BtreeLeaveAll(db);

@@ -3666,6 +3666,9 @@ static int sqliteCmdUsage(
    "HANDLE ?FILENAME? ?-vfs VFSNAME? ?-readonly BOOLEAN? ?-create BOOLEAN?"
    " ?-nofollow BOOLEAN?"
    " ?-nomutex BOOLEAN? ?-fullmutex BOOLEAN? ?-uri BOOLEAN?"
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+    " ?-shared-schema BOOLEAN?"
+#endif
  );
  return TCL_ERROR;
 }
@@ -3797,6 +3800,16 @@ static int SQLITE_TCLAPI DbMain(
      }else{
        flags &= ~SQLITE_OPEN_URI;
      }
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+    }else if( strcmp(zArg, "-shared-schema")==0 ){
+      int b;
+      if( Tcl_GetBooleanFromObj(interp, objv[i], &b) ) return TCL_ERROR;
+      if( b ){
+        flags |= SQLITE_OPEN_SHARED_SCHEMA;
+      }else{
+        flags &= ~SQLITE_OPEN_SHARED_SCHEMA;
+      }
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
    }else if( strcmp(zArg, "-translatefilename")==0 ){
      if( Tcl_GetBooleanFromObj(interp, objv[i], &bTranslateFileName) ){
        return TCL_ERROR;
@@ -764,6 +764,12 @@ Tcl_SetVar2(interp, "sqlite_options", "mergesort", "1", TCL_GLOBAL_ONLY);
  Tcl_SetVar2(interp, "sqlite_options", "windowfunc", "1", TCL_GLOBAL_ONLY);
 #endif

+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  Tcl_SetVar2(interp, "sqlite_options", "sharedschema", "1", TCL_GLOBAL_ONLY);
+#else
+  Tcl_SetVar2(interp, "sqlite_options", "sharedschema", "0", TCL_GLOBAL_ONLY);
+#endif
+
 #define LINKVAR(x) { \
    static const int cv_ ## x = SQLITE_ ## x; \
    Tcl_LinkVar(interp, "SQLITE_" #x, (char *)&(cv_ ## x), \
@@ -0,0 +1,282 @@
+/*
+** 2006 June 10
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+** Code for testing the virtual table interfaces.  This code
+** is not included in the SQLite library.  It is used for automated
+** testing of the SQLite library.
+*/
+
+/*
+** None of this works unless we have virtual tables.
+*/
+#if !defined(SQLITE_OMIT_VIRTUALTABLE) && defined(SQLITE_TEST)
+
+#include <tcl.h>
+
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+
+#include "sqliteInt.h"
+
+/* The code in this file defines a sqlite3 virtual-table module with
+** the following schema.
+*/
+#define SCHEMAPOOL_SCHEMA \
+"CREATE TABLE x("         \
+"  cksum   INTEGER, "     \
+"  nref    INTEGER, "     \
+"  nschema INTEGER, "     \
+"  ndelete INTEGER  "     \
+")"
+
+#define SCHEMAPOOL_NFIELD 4
+
+typedef struct schemapool_vtab schemapool_vtab;
+typedef struct schemapool_cursor schemapool_cursor;
+
+/* A schema table object */
+struct schemapool_vtab {
+  sqlite3_vtab base;
+};
+
+/* A schema table cursor object */
+struct schemapool_cursor {
+  sqlite3_vtab_cursor base;
+  sqlite3_int64 *aData;
+  int iRow;
+  int nRow;
+};
+
+/*
+** Table destructor for the schema module.
+*/
+static int schemaPoolDestroy(sqlite3_vtab *pVtab){
+  sqlite3_free(pVtab);
+  return 0;
+}
+
+/*
+** Table constructor for the schema module.
+*/
+static int schemaPoolCreate(
+  sqlite3 *db,
+  void *pAux,
+  int argc, const char *const*argv,
+  sqlite3_vtab **ppVtab,
+  char **pzErr
+){
+  int rc = SQLITE_NOMEM;
+  schemapool_vtab *pVtab = sqlite3_malloc(sizeof(schemapool_vtab));
+  if( pVtab ){
+    memset(pVtab, 0, sizeof(schemapool_vtab));
+    rc = sqlite3_declare_vtab(db, SCHEMAPOOL_SCHEMA);
+    if( rc!=SQLITE_OK ){
+      sqlite3_free(pVtab);
+      pVtab = 0;
+    }
+  }
+  *ppVtab = (sqlite3_vtab *)pVtab;
+  return rc;
+}
+
+/*
+** Open a new cursor on the schema table.
+*/
+static int schemaPoolOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
+  int rc = SQLITE_NOMEM;
+  schemapool_cursor *pCur;
+  pCur = sqlite3_malloc(sizeof(schemapool_cursor));
+  if( pCur ){
+    memset(pCur, 0, sizeof(schemapool_cursor));
+    *ppCursor = (sqlite3_vtab_cursor*)pCur;
+    rc = SQLITE_OK;
+  }
+  return rc;
+}
+
+/*
+** Close a schema table cursor.
+*/
+static int schemaPoolClose(sqlite3_vtab_cursor *cur){
+  schemapool_cursor *pCur = (schemapool_cursor*)cur;
+  sqlite3_free(pCur->aData);
+  sqlite3_free(pCur);
+  return SQLITE_OK;
+}
+
+/*
+** Retrieve a column of data.
+*/
+static int schemaPoolColumn(sqlite3_vtab_cursor *cur, sqlite3_context *ctx, int i){
+  schemapool_cursor *pCur = (schemapool_cursor*)cur;
+  assert( i==0 || i==1 || i==2 || i==3 );
+  sqlite3_result_int64(ctx, pCur->aData[pCur->iRow*SCHEMAPOOL_NFIELD + i]);
+  return SQLITE_OK;
+}
+
+/*
+** Retrieve the current rowid.
+*/
+static int schemaPoolRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *pRowid){
+  schemapool_cursor *pCur = (schemapool_cursor*)cur;
+  *pRowid = pCur->iRow + 1;
+  return SQLITE_OK;
+}
+
+static int schemaPoolEof(sqlite3_vtab_cursor *cur){
+  schemapool_cursor *pCur = (schemapool_cursor*)cur;
+  return pCur->iRow>=pCur->nRow;
+}
+
+/*
+** Advance the cursor to the next row.
+*/
+static int schemaPoolNext(sqlite3_vtab_cursor *cur){
+  schemapool_cursor *pCur = (schemapool_cursor*)cur;
+  pCur->iRow++;
+  return SQLITE_OK;
+}
+
+struct SchemaPool {
+  int nRef;                       /* Number of pointers to this object */
+  int nDelete;                    /* Schema objects deleted by ReleaseAll() */
+  u64 cksum;                      /* Checksum for this Schema contents */
+  Schema *pSchema;                /* Linked list of Schema objects */
+  Schema sSchema;                 /* The single dummy schema object */
+  SchemaPool *pNext;              /* Next element in schemaPoolList */
+};
+extern SchemaPool *sqlite3SchemaPoolList(void);
+
+/*
+** Reset a schemaPool table cursor.
+*/
+static int schemaPoolFilter(
+  sqlite3_vtab_cursor *pVtabCursor, 
+  int idxNum, const char *idxStr,
+  int argc, sqlite3_value **argv
+){
+  SchemaPool *pSPool;
+  schemapool_cursor *pCur = (schemapool_cursor*)pVtabCursor;
+
+  sqlite3_free(pCur->aData);
+  pCur->aData = 0;
+  pCur->nRow = 0;
+  pCur->iRow = 0;
+
+  for(pSPool = sqlite3SchemaPoolList(); pSPool; pSPool=pSPool->pNext){
+    pCur->nRow++;
+  }
+
+  if( pCur->nRow ){
+    int iRow = 0;
+    int nByte = SCHEMAPOOL_NFIELD * pCur->nRow * sizeof(i64);
+    pCur->aData = (i64*)sqlite3_malloc(nByte);
+    if( pCur->aData==0 ) return SQLITE_NOMEM;
+    for(pSPool = sqlite3SchemaPoolList(); pSPool; pSPool=pSPool->pNext){
+      Schema *p;
+      i64 nSchema = 0;
+      for(p=pSPool->pSchema; p; p=p->pNext){
+        nSchema++;
+      }
+      pCur->aData[0 + iRow*SCHEMAPOOL_NFIELD] = pSPool->cksum;
+      pCur->aData[1 + iRow*SCHEMAPOOL_NFIELD] = (i64)pSPool->nRef;
+      pCur->aData[2 + iRow*SCHEMAPOOL_NFIELD] = nSchema;
+      pCur->aData[3 + iRow*SCHEMAPOOL_NFIELD] = (i64)pSPool->nDelete;
+      iRow++;
+    }
+  }
+
+  return SQLITE_OK;
+}
+
+/*
+** Analyse the WHERE condition.
+*/
+static int schemaPoolBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo){
+  return SQLITE_OK;
+}
+
+/*
+** A virtual table module that merely echos method calls into TCL
+** variables.
+*/
+static sqlite3_module schemaPoolModule = {
+  0,                           /* iVersion */
+  schemaPoolCreate,
+  schemaPoolCreate,
+  schemaPoolBestIndex,
+  schemaPoolDestroy,
+  schemaPoolDestroy,
+  schemaPoolOpen,              /* xOpen - open a cursor */
+  schemaPoolClose,             /* xClose - close a cursor */
+  schemaPoolFilter,            /* xFilter - configure scan constraints */
+  schemaPoolNext,              /* xNext - advance a cursor */
+  schemaPoolEof,               /* xEof */
+  schemaPoolColumn,            /* xColumn - read data */
+  schemaPoolRowid,             /* xRowid - read data */
+  0,                           /* xUpdate */
+  0,                           /* xBegin */
+  0,                           /* xSync */
+  0,                           /* xCommit */
+  0,                           /* xRollback */
+  0,                           /* xFindMethod */
+  0,                           /* xRename */
+};
+
+/*
+** Decode a pointer to an sqlite3 object.
+*/
+extern int getDbPointer(Tcl_Interp *interp, const char *zA, sqlite3 **ppDb);
+
+/*
+** Register the schema virtual table module.
+*/
+static int SQLITE_TCLAPI register_schemapool_module(
+  ClientData clientData, /* Not used */
+  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
+  int objc,              /* Number of arguments */
+  Tcl_Obj *CONST objv[]  /* Command arguments */
+){
+  sqlite3 *db;
+  if( objc!=2 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "DB");
+    return TCL_ERROR;
+  }
+  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
+#ifndef SQLITE_OMIT_VIRTUALTABLE
+  sqlite3_create_module(db, "schemapool", &schemaPoolModule, 0);
+#endif
+  return TCL_OK;
+}
+
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+#endif /* !defined(SQLITE_OMIT_VIRTUALTABLE) && defined(SQLITE_TEST) */
+
+/*
+** Register commands with the TCL interpreter.
+*/
+int Sqlitetestschemapool_Init(Tcl_Interp *interp){
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  static struct {
+     char *zName;
+     Tcl_ObjCmdProc *xProc;
+     void *clientData;
+  } aObjCmd[] = {
+     { "register_schemapool_module", register_schemapool_module, 0 },
+  };
+  int i;
+  for(i=0; i<sizeof(aObjCmd)/sizeof(aObjCmd[0]); i++){
+    Tcl_CreateObjCommand(interp, aObjCmd[i].zName, 
+        aObjCmd[i].xProc, aObjCmd[i].clientData, 0);
+  }
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+  return TCL_OK;
+}
+
@@ -77,6 +77,7 @@ const char *sqlite3TestInit(Tcl_Interp *interp){
  extern int Sqlitetest_malloc_Init(Tcl_Interp*);
  extern int Sqlitetest_mutex_Init(Tcl_Interp*);
  extern int Sqlitetestschema_Init(Tcl_Interp*);
+  extern int Sqlitetestschemapool_Init(Tcl_Interp*);
  extern int Sqlitetestsse_Init(Tcl_Interp*);
  extern int Sqlitetesttclvar_Init(Tcl_Interp*);
  extern int Sqlitetestfs_Init(Tcl_Interp*);
@@ -147,6 +148,7 @@ const char *sqlite3TestInit(Tcl_Interp *interp){
  Sqlitetest_malloc_Init(interp);
  Sqlitetest_mutex_Init(interp);
  Sqlitetestschema_Init(interp);
+  Sqlitetestschemapool_Init(interp);
  Sqlitetesttclvar_Init(interp);
  Sqlitetestfs_Init(interp);
  SqlitetestThread_Init(interp);
@@ -564,6 +564,7 @@ int sqlite3RunParser(Parse *pParse, const char *zSql, char **pzErrMsg){
  int lastTokenParsed = -1;       /* type of the previous token */
  sqlite3 *db = pParse->db;       /* The database connection */
  int mxSqlLen;                   /* Max length of an SQL string */
+  Parse *pParentParse = db->pParse;
 #ifdef sqlite3Parser_ENGINEALWAYSONSTACK
  yyParser sEngine;    /* Space to hold the Lemon-generated Parser object */
 #endif
@@ -599,7 +600,6 @@ int sqlite3RunParser(Parse *pParse, const char *zSql, char **pzErrMsg){
  assert( pParse->pNewTrigger==0 );
  assert( pParse->nVar==0 );
  assert( pParse->pVList==0 );
-  pParse->pParentParse = db->pParse;
  db->pParse = pParse;
  while( 1 ){
    n = sqlite3GetToken((u8*)zSql, &tokenType);
@@ -726,8 +726,7 @@ int sqlite3RunParser(Parse *pParse, const char *zSql, char **pzErrMsg){
    pParse->pZombieTab = p->pNextZombie;
    sqlite3DeleteTable(db, p);
  }
-  db->pParse = pParse->pParentParse;
-  pParse->pParentParse = 0;
+  db->pParse = pParentParse;
  assert( nErr==0 || pParse->rc!=SQLITE_OK );
  return nErr;
 }
@@ -56,15 +56,30 @@ Trigger *sqlite3TriggerList(Parse *pParse, Table *pTab){
  }

  if( pTmpSchema!=pTab->pSchema ){
+    sqlite3 *db = pParse->db;
    HashElem *p;
-    assert( sqlite3SchemaMutexHeld(pParse->db, 0, pTmpSchema) );
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+    char *zSchema = 0;
+    if( IsSharedSchema(db) ){
+      zSchema = db->aDb[sqlite3SchemaToIndex(db, pTab->pSchema)].zDbSName;
+    }
+#endif
+    assert( sqlite3SchemaMutexHeld(db, 0, pTmpSchema) );
    for(p=sqliteHashFirst(&pTmpSchema->trigHash); p; p=sqliteHashNext(p)){
      Trigger *pTrig = (Trigger *)sqliteHashData(p);
-      if( pTrig->pTabSchema==pTab->pSchema
-       && 0==sqlite3StrICmp(pTrig->table, pTab->zName) 
-      ){
-        pTrig->pNext = (pList ? pList : pTab->pTrigger);
-        pList = pTrig;
+
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+      if( (zSchema==0 && pTrig->pTabSchema==pTab->pSchema)
+       || (zSchema!=0 && 0==sqlite3StrICmp(pTrig->zTabSchema, zSchema)) )
+#else 
+      if( pTrig->pTabSchema==pTab->pSchema )
+#endif
+      {
+        if( 0==sqlite3StrICmp(pTrig->table, pTab->zName) ){
+          pTrig->pTabSchema = pTab->pSchema;
+          pTrig->pNext = (pList ? pList : pTab->pTrigger);
+          pList = pTrig;
+        }
      }
    }
  }
@@ -238,6 +253,12 @@ void sqlite3BeginTrigger(
  pTrigger->zName = zName;
  zName = 0;
  pTrigger->table = sqlite3DbStrDup(db, pTableName->a[0].zName);
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  if( IsSharedSchema(db) && iDb==1 ){
+    int iTabDb = sqlite3SchemaToIndex(db, pTab->pSchema);
+    pTrigger->zTabSchema = sqlite3DbStrDup(db, db->aDb[iTabDb].zDbSName);
+  }
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
  pTrigger->pSchema = db->aDb[iDb].pSchema;
  pTrigger->pTabSchema = pTab->pSchema;
  pTrigger->op = (u8)op;
@@ -344,7 +365,7 @@ void sqlite3FinishTrigger(
       pTrig->table, z);
    sqlite3DbFree(db, z);
    sqlite3ChangeCookie(pParse, iDb);
-    sqlite3VdbeAddParseSchemaOp(v, iDb,
+    sqlite3VdbeAddParseSchemaOp(pParse, iDb,
        sqlite3MPrintf(db, "type='trigger' AND name='%q'", zName));
  }

@@ -562,6 +583,9 @@ void sqlite3DeleteTrigger(sqlite3 *db, Trigger *pTrigger){
  sqlite3DeleteTriggerStep(db, pTrigger->step_list);
  sqlite3DbFree(db, pTrigger->zName);
  sqlite3DbFree(db, pTrigger->table);
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  sqlite3DbFree(db, pTrigger->zTabSchema);
+#endif
  sqlite3ExprDelete(db, pTrigger->pWhen);
  sqlite3IdListDelete(db, pTrigger->pColumns);
  sqlite3DbFree(db, pTrigger);
@@ -633,6 +657,7 @@ void sqlite3DropTriggerPtr(Parse *pParse, Trigger *pTrigger){

  iDb = sqlite3SchemaToIndex(pParse->db, pTrigger->pSchema);
  assert( iDb>=0 && iDb<db->nDb );
+  sqlite3SchemaWritable(pParse, iDb);
  pTable = tableOfTrigger(pTrigger);
  assert( (pTable && pTable->pSchema==pTrigger->pSchema) || iDb==1 );
 #ifndef SQLITE_OMIT_AUTHORIZATION
@@ -125,6 +125,7 @@ void sqlite3Vacuum(Parse *pParse, Token *pNm, Expr *pInto){
  }
  if( iDb!=1 ){
    int iIntoReg = 0;
+    sqlite3SchemaWritable(pParse, iDb);
    if( pInto && sqlite3ResolveSelfReference(pParse,0,0,pInto,0)==0 ){
      iIntoReg = ++pParse->nMem;
      sqlite3ExprCode(pParse, pInto, iIntoReg);
@@ -3572,13 +3572,6 @@ case OP_Transaction: {
   && (iMeta!=pOp->p3
      || db->aDb[pOp->p1].pSchema->iGeneration!=pOp->p4.i)
  ){
-    /*
-    ** IMPLEMENTATION-OF: R-03189-51135 As each SQL statement runs, the schema
-    ** version is checked to ensure that the schema has not changed since the
-    ** SQL statement was prepared.
-    */
-    sqlite3DbFree(db, p->zErrMsg);
-    p->zErrMsg = sqlite3DbStrDup(db, "database schema has changed");
    /* If the schema-cookie from the database file matches the cookie 
    ** stored with the in-memory representation of the schema, do
    ** not reload the schema from the database file.
@@ -3595,6 +3588,13 @@ case OP_Transaction: {
    if( db->aDb[pOp->p1].pSchema->schema_cookie!=iMeta ){
      sqlite3ResetOneSchema(db, pOp->p1);
    }
+    /*
+    ** IMPLEMENTATION-OF: R-03189-51135 As each SQL statement runs, the schema
+    ** version is checked to ensure that the schema has not changed since the
+    ** SQL statement was prepared.
+    */
+    sqlite3DbFree(db, p->zErrMsg);
+    p->zErrMsg = sqlite3DbStrDup(db, "database schema has changed");
    p->expired = 1;
    rc = SQLITE_SCHEMA;
  }
@@ -223,7 +223,7 @@ VdbeOp *sqlite3VdbeAddOpList(Vdbe*, int nOp, VdbeOpList const *aOp,int iLineno);
 #else
 # define sqlite3ExplainBreakpoint(A,B) /*no-op*/
 #endif
-void sqlite3VdbeAddParseSchemaOp(Vdbe*,int,char*);
+void sqlite3VdbeAddParseSchemaOp(Parse*,int,char*);
 void sqlite3VdbeChangeOpcode(Vdbe*, int addr, u8);
 void sqlite3VdbeChangeP1(Vdbe*, int addr, int P1);
 void sqlite3VdbeChangeP2(Vdbe*, int addr, int P2);
@@ -471,8 +471,10 @@ void sqlite3VdbeExplainPop(Parse *pParse){
 ** The zWhere string must have been obtained from sqlite3_malloc().
 ** This routine will take ownership of the allocated memory.
 */
-void sqlite3VdbeAddParseSchemaOp(Vdbe *p, int iDb, char *zWhere){
+void sqlite3VdbeAddParseSchemaOp(Parse *pParse, int iDb, char *zWhere){
+  Vdbe *p = pParse->pVdbe;
  int j;
+  sqlite3SchemaWritable(pParse, iDb);
  sqlite3VdbeAddOp4(p, OP_ParseSchema, iDb, 0, 0, zWhere, P4_DYNAMIC);
  for(j=0; j<p->db->nDb; j++) sqlite3VdbeUsesBtree(p, j);
  sqlite3MayAbort(p->pParse);
@@ -131,7 +131,9 @@ int sqlite3_blob_open(
  char *zErr = 0;
  Table *pTab;
  Incrblob *pBlob = 0;
+  Parse *pParentParse = db->pParse;
  Parse sParse;
+  int bUnlock;            /* True to unlock reusable schemas before returning */

 #ifdef SQLITE_ENABLE_API_ARMOR
  if( ppBlob==0 ){
@@ -148,11 +150,13 @@ int sqlite3_blob_open(

  sqlite3_mutex_enter(db->mutex);

+  bUnlock = sqlite3LockReusableSchema(db);
  pBlob = (Incrblob *)sqlite3DbMallocZero(db, sizeof(Incrblob));
  do {
    memset(&sParse, 0, sizeof(Parse));
    if( !pBlob ) goto blob_open_out;
    sParse.db = db;
+    db->pParse = &sParse;
    sqlite3DbFree(db, zErr);
    zErr = 0;

@@ -331,6 +335,8 @@ int sqlite3_blob_open(
  } while( (++nAttempt)<SQLITE_MAX_SCHEMA_RETRY && rc==SQLITE_SCHEMA );

 blob_open_out:
+  db->pParse = pParentParse;
+  sqlite3UnlockReusableSchema(db, bUnlock);
  if( rc==SQLITE_OK && db->mallocFailed==0 ){
    *ppBlob = (sqlite3_blob *)pBlob;
  }else{
@@ -192,6 +192,24 @@ void sqlite3VtabLock(VTable *pVTab){
 VTable *sqlite3GetVTable(sqlite3 *db, Table *pTab){
  VTable *pVtab;
  assert( IsVirtual(pTab) );
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  if( IsSharedSchema(db) ){
+    int iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
+    if( iDb!=1 ){
+      VTable **pp;
+      for(pp=&db->aDb[iDb].pVTable; *pp; pp=&(*pp)->pNext){
+        if( sqlite3StrICmp(pTab->zName, (*pp)->zName)==0 ) break;
+      }
+      pVtab = *pp;
+      if( pVtab && pTab->nCol<=0 ){
+        *pp = pVtab->pNext;
+        sqlite3VtabUnlock(pVtab);
+        pVtab = 0;
+      }
+      return pVtab;
+    }
+  }
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
  for(pVtab=pTab->pVTable; pVtab && pVtab->db!=db; pVtab=pVtab->pNext);
  return pVtab;
 }
@@ -489,7 +507,7 @@ void sqlite3VtabFinishParse(Parse *pParse, Token *pEnd){

    sqlite3VdbeAddOp0(v, OP_Expire);
    zWhere = sqlite3MPrintf(db, "name=%Q AND sql=%Q", pTab->zName, zStmt);
-    sqlite3VdbeAddParseSchemaOp(v, iDb, zWhere);
+    sqlite3VdbeAddParseSchemaOp(pParse, iDb, zWhere);
    sqlite3DbFree(db, zStmt);

    iReg = ++pParse->nMem;
@@ -563,6 +581,7 @@ static int vtabCallConstructor(
  char *zModuleName;
  int iDb;
  VtabCtx *pCtx;
+  int nByte;                      /* Bytes of space to allocate */

  /* Check that the virtual-table is not already being initialized */
  for(pCtx=db->pVtabCtx; pCtx; pCtx=pCtx->pPrior){
@@ -579,7 +598,11 @@ static int vtabCallConstructor(
    return SQLITE_NOMEM_BKPT;
  }

-  pVTable = sqlite3MallocZero(sizeof(VTable));
+  nByte = sizeof(VTable);
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  nByte += sqlite3Strlen30(pTab->zName) + 1;
+#endif
+  pVTable = (VTable*)sqlite3MallocZero(nByte);
  if( !pVTable ){
    sqlite3OomFault(db);
    sqlite3DbFree(db, zModuleName);
@@ -587,6 +610,10 @@ static int vtabCallConstructor(
  }
  pVTable->db = db;
  pVTable->pMod = pMod;
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+  pVTable->zName = (char*)&pVTable[1];
+  memcpy(pVTable->zName, pTab->zName, nByte-sizeof(VTable));
+#endif
  pVTable->eVtabRisk = SQLITE_VTABRISK_Normal;

  iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
@@ -629,12 +656,22 @@ static int vtabCallConstructor(
      int iCol;
      u16 oooHidden = 0;
      /* If everything went according to plan, link the new VTable structure
-      ** into the linked list headed by pTab->pVTable. Then loop through the 
-      ** columns of the table to see if any of them contain the token "hidden".
-      ** If so, set the Column COLFLAG_HIDDEN flag and remove the token from
-      ** the type string.  */
-      pVTable->pNext = pTab->pVTable;
-      pTab->pVTable = pVTable;
+      ** into the linked list headed by pTab->pVTable. Or, if this is a
+      ** reusable schema, into the linked list headed by Db.pVTable.
+      **
+      ** Then loop through the columns of the table to see if any of them
+      ** contain the token "hidden". If so, set the Column COLFLAG_HIDDEN flag
+      ** and remove the token from the type string.  */
+#ifdef SQLITE_ENABLE_SHARED_SCHEMA
+      if( IsSharedSchema(db) && iDb!=1 ){
+        pVTable->pNext = db->aDb[iDb].pVTable;
+        db->aDb[iDb].pVTable = pVTable;
+      }else
+#endif /* ifdef SQLITE_ENABLE_SHARED_SCHEMA */
+      {
+        pVTable->pNext = pTab->pVTable;
+        pTab->pVTable = pVTable;
+      }

      for(iCol=0; iCol<pTab->nCol; iCol++){
        char *zType = sqlite3ColumnType(&pTab->aCol[iCol], "");
@@ -687,6 +724,7 @@ int sqlite3VtabCallConnect(Parse *pParse, Table *pTab){

  assert( pTab );
  if( !IsVirtual(pTab) || sqlite3GetVTable(db, pTab) ){
+    assert( !IsVirtual(pTab) || pTab->nCol>0 );
    return SQLITE_OK;
  }

@@ -65,8 +65,8 @@ foreach {tn sql1 sql2} {
  3 "SELECT a, sum(b) FROM t1 GROUP BY a COLLATE binary HAVING a=2"
    "SELECT a, sum(b) FROM t1 WHERE a=2 GROUP BY a COLLATE binary"

-  5 "SELECT a, sum(b) FROM t1 GROUP BY a COLLATE binary HAVING 0"
-    "SELECT a, sum(b) FROM t1 WHERE 0 GROUP BY a COLLATE binary"
+  5 "SELECT a, sum(b) FROM t1 GROUP BY a COLLATE binary HAVING 1"
+    "SELECT a, sum(b) FROM t1 WHERE 1 GROUP BY a COLLATE binary"

  6 "SELECT count(*) FROM t1,t2 WHERE a=c GROUP BY b, d HAVING b=d"
    "SELECT count(*) FROM t1,t2 WHERE a=c AND b=d GROUP BY b, d"
@@ -154,5 +154,25 @@ do_execsql_test 4.3 {
  SELECT a, sum(b) FROM t3 WHERE nondeter(a) GROUP BY a
 } {1 4 2 2}

+#-------------------------------------------------------------------------
+reset_db
+do_execsql_test 5.0 {
+  CREATE TABLE t1(a, b);
+  CREATE TABLE t2(x, y);
+  INSERT INTO t1 VALUES('a', 'b');
+}
+
+# The WHERE clause (a=2), uses an aggregate column from the outer query.
+# If the HAVING term (0) is moved into the WHERE clause in this case,
+# SQLite would at one point optimize (a=2 AND 0) to simply (0). Which
+# is logically correct, but happened to cause problems in aggregate
+# processing for the outer query. This test case verifies that those 
+# problems are no longer present.
+do_execsql_test 5.1 {
+  SELECT min(b), (
+    SELECT x FROM t2 WHERE a=2 GROUP BY y HAVING 0
+  ) FROM t1;
+} {b {}}
+

 finish_test
@@ -0,0 +1,394 @@
+# 2017 August 9
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+#
+
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix reuse1
+
+ifcapable !sharedschema {
+  finish_test
+  return
+}
+
+forcedelete test.db2
+sqlite3 db2 test.db2
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(x INTEGER PRIMARY KEY, y UNIQUE, z);
+  CREATE INDEX i1 ON t1(z);
+  PRAGMA schema_version;
+} {2}
+
+do_execsql_test -db db2 1.1 {
+  CREATE TABLE t1(x INTEGER PRIMARY KEY, y UNIQUE, z);
+  CREATE INDEX i1 ON t1(z);
+  PRAGMA schema_version;
+} {2}
+
+do_test 1.2 {
+  db close
+  db2 close
+  sqlite3 db2 test.db2 -shared-schema 1
+  sqlite3 db  test.db -shared-schema 1
+} {}
+
+do_execsql_test -db db2 1.3.1 {
+  INSERT INTO t1 VALUES(1, 2, 3);
+  INSERT INTO t1 VALUES(4, 5, 6);
+}
+
+do_execsql_test 1.3.2 {
+  SELECT * FROM t1;
+  PRAGMA integrity_check;
+} {ok}
+
+do_execsql_test -db db2 1.3.3 {
+  SELECT * FROM t1;
+  PRAGMA integrity_check;
+} {1 2 3 4 5 6 ok}
+
+sqlite3 db3 test.db2
+do_execsql_test -db db3 1.4.1 {
+  ALTER TABLE t1 ADD COLUMN a;
+}
+do_execsql_test -db db2 1.4.2 {
+  SELECT * FROM t1;
+} {1 2 3 {} 4 5 6 {}}
+do_execsql_test 1.4.3 {
+  SELECT * FROM t1;
+} {}
+
+db3 close
+sqlite3 db3 test.db
+do_execsql_test -db db3 1.5.0 {
+  CREATE TRIGGER tr1 AFTER INSERT ON t1 BEGIN
+    SELECT 1, 2, 3;
+  END;
+}
+
+# Check that the schema cannot be modified if the db was opened with
+# SQLITE_OPEN_REUSE_SCHEMA.
+#
+foreach {tn sql} {
+  1  { CREATE TABLE t2(x, y) }
+  2  { CREATE INDEX i2 ON t1(z) }
+  3  { CREATE VIEW v2 AS SELECT * FROM t2 }
+  4  { ALTER TABLE t1 RENAME TO t3 }
+  5  { ALTER TABLE t1 ADD COLUMN xyz }
+  6  { VACUUM }
+  7  { DROP INDEX i1 }
+  8  { DROP TABLE t1 }
+  9  { DROP TRIGGER tr1 }
+  10 { ANALYZE }
+  11 { ALTER TABLE t1 RENAME z TO zzz }
+} {
+  do_catchsql_test 1.5.$tn $sql {1 {attempt to modify read-only schema}}
+}
+
+#-------------------------------------------------------------------------
+#
+reset_db
+forcedelete test.db2
+ifcapable fts5 {
+  do_execsql_test 2.0 {
+    CREATE VIRTUAL TABLE ft USING fts5(a);
+    INSERT INTO ft VALUES('one'), ('two'), ('three');
+    ATTACH 'test.db2' AS aux;
+    CREATE VIRTUAL TABLE aux.ft USING fts5(a);
+    INSERT INTO aux.ft VALUES('aux1'), ('aux2'), ('aux3');
+  }
+
+  db close
+  sqlite3 db  test.db -shared-schema 1
+
+  do_execsql_test 2.1 {
+    ATTACH 'test.db2' AS aux;
+    SELECT * FROM main.ft;
+  } {one two three}
+
+breakpoint
+  do_execsql_test 2.2 {
+    SELECT * FROM aux.ft;
+  } {aux1 aux2 aux3}
+
+  do_execsql_test 2.2 {
+    SELECT * FROM aux.ft_content;
+  } {1 aux1 2 aux2 3 aux3}
+}
+
+#-------------------------------------------------------------------------
+#
+reset_db
+forcedelete test.db2
+do_execsql_test 3.0 {
+  CREATE TABLE t1(a PRIMARY KEY, b, c);
+  CREATE VIEW v1 AS SELECT * FROM t1;
+  CREATE TRIGGER v1_ins INSTEAD OF INSERT ON v1 BEGIN
+    INSERT INTO t1 VALUES(new.a, new.b, new.c);
+  END;
+  CREATE TRIGGER v1_del INSTEAD OF DELETE ON v1 BEGIN
+    DELETE FROM t1 WHERE a=old.a;
+  END;
+  CREATE TRIGGER v1_up INSTEAD OF UPDATE ON v1 BEGIN
+    UPDATE t1 SET a=new.a, b=new.b, c=new.c WHERE a=old.a;
+  END;
+}
+forcecopy test.db test.db2
+
+do_test 3.1 {
+  sqlite3 db2 test.db2
+  execsql { INSERT INTO t1 VALUES(1, 2, 3) } db
+  execsql { INSERT INTO t1 VALUES(4, 5, 6) } db2
+  db2 close
+  execsql { ATTACH 'test.db2' AS aux; }
+} {}
+
+do_execsql_test 3.2 {
+  SELECT * FROM main.v1;
+} {1 2 3}
+
+do_execsql_test 3.3 {
+  SELECT * FROM aux.v1;
+} {4 5 6}
+
+db close
+sqlite3 db test.db -shared-schema 1
+
+do_execsql_test 3.4 { ATTACH 'test.db2' AS aux } {}
+do_execsql_test 3.5 { SELECT * FROM main.v1 } {1 2 3}
+do_execsql_test 3.6 { SELECT * FROM aux.v1  } {4 5 6}
+
+do_execsql_test 3.7.1 { INSERT INTO aux.t1 VALUES(8, 9, 10); }
+do_execsql_test 3.7.2 { SELECT * FROM main.v1 } {1 2 3}
+do_execsql_test 3.7.3 { SELECT * FROM aux.v1  } {4 5 6 8 9 10}
+
+do_execsql_test 3.8.1 { DELETE FROM aux.t1 WHERE b=5 }
+do_execsql_test 3.8.2 { SELECT * FROM main.v1 } {1 2 3}
+do_execsql_test 3.8.3 { SELECT * FROM aux.v1  } {8 9 10}
+
+do_execsql_test 3.9.1 { UPDATE aux.t1 SET b='abc' }
+do_execsql_test 3.9.2 { SELECT * FROM main.v1 } {1 2 3}
+do_execsql_test 3.9.3 { SELECT * FROM aux.v1  } {8 abc 10}
+
+do_execsql_test 3.10.1 { INSERT INTO aux.v1 VALUES(11, 12, 13) }
+do_execsql_test 3.10.2 { SELECT * FROM main.v1 } {1 2 3}
+do_execsql_test 3.10.3 { SELECT * FROM aux.v1  } {8 abc 10 11 12 13}
+
+do_execsql_test 3.11.1 { DELETE FROM aux.v1 WHERE b='abc' }
+do_execsql_test 3.11.2 { SELECT * FROM main.v1 } {1 2 3}
+do_execsql_test 3.11.3 { SELECT * FROM aux.v1  } {11 12 13}
+
+do_execsql_test 3.12.1 { UPDATE aux.v1 SET b='def' }
+do_execsql_test 3.12.2 { SELECT * FROM main.v1 } {1 2 3}
+do_execsql_test 3.12.3 { SELECT * FROM aux.v1  } {11 def 13}
+
+do_execsql_test 3.13.1 {
+  CREATE TEMP TRIGGER xyz AFTER INSERT ON aux.t1 BEGIN
+    INSERT INTO v1 VALUES(new.a, new.b, new.c);
+  END
+}
+do_execsql_test 3.13.2 {
+  INSERT INTO aux.v1 VALUES('x', 'y', 'z');
+}
+do_execsql_test 3.13.3 {
+  SELECT * FROM v1;
+} {1 2 3 x y z}
+
+#-------------------------------------------------------------------------
+#
+reset_db
+forcedelete test.db2
+do_execsql_test 4.0 {
+  CREATE TABLE t1(a PRIMARY KEY, b, c UNIQUE);
+  CREATE TABLE del(a, b, c);
+  CREATE TRIGGER tr1 AFTER DELETE ON t1 BEGIN
+    INSERT INTO del VALUES(old.a, old.b, old.c);
+  END;
+}
+forcecopy test.db test.db2
+
+db close
+sqlite3 db test.db -shared-schema 1
+execsql { 
+  ATTACH 'test.db2' AS aux;
+  PRAGMA recursive_triggers = 1;
+}
+
+do_execsql_test 4.1 {
+  INSERT INTO main.t1 VALUES(1, 2, 3);
+  INSERT INTO aux.t1 VALUES(4, 5, 6);
+}
+
+do_execsql_test 4.2.1 {
+  INSERT OR REPLACE INTO aux.t1 VALUES('a', 'b', 6);
+  SELECT * FROM aux.t1;
+} {a b 6}
+do_execsql_test 4.2.2 { SELECT * FROM aux.del  } {4 5 6}
+do_execsql_test 4.2.3 { SELECT * FROM main.del } {}
+
+do_execsql_test 4.3.1 {
+  INSERT INTO aux.t1 VALUES('x', 'y', 'z');
+  UPDATE OR REPLACE aux.t1 SET c='z' WHERE a='a';
+} {}
+do_execsql_test 4.3.2 { SELECT * FROM aux.del  } {4 5 6 x y z}
+do_execsql_test 4.3.3 { SELECT * FROM main.del } {}
+
+#-------------------------------------------------------------------------
+#
+reset_db
+do_execsql_test 5.0 {
+  CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
+  CREATE TABLE t2(a INTEGER PRIMARY KEY, b, c);
+  CREATE INDEX i1 ON t1(b);
+  INSERT INTO t1 VALUES(1, 2, 3), (4, 5, 6);
+  ANALYZE;
+  PRAGMA writable_schema = 1;
+  DELETE FROM sqlite_stat1;
+}
+db close
+forcecopy test.db test.db2
+sqlite3 db test.db -shared-schema 1
+execsql { ATTACH 'test.db2' AS aux }
+
+foreach {tn sql} {
+  1 { CREATE TABLE t3(x) }
+  2 { DROP TABLE t2 }
+  3 { CREATE INDEX i2 ON t2(b) }
+  4 { DROP INDEX i1 }
+  5 { ALTER TABLE t1 ADD COLUMN d }
+  6 { ALTER TABLE t1 RENAME TO t3 }
+  7 { ALTER TABLE t1 RENAME c TO d }
+} {
+  do_catchsql_test 5.1.$tn $sql {1 {attempt to modify read-only schema}}
+}
+
+do_execsql_test 5.2.1 { ANALYZE aux.t1 } {}
+do_execsql_test 5.2.2 { SELECT * FROM aux.sqlite_stat1  } {t1 i1 {2 1}}
+do_execsql_test 5.2.3 { SELECT * FROM main.sqlite_stat1 } {}
+
+do_test 5.3.0 {
+  sqlite3 db2 test.db2
+  db2 eval { 
+    PRAGMA writable_schema = 1;
+    DELETE FROM sqlite_stat1;
+  }
+} {}
+
+do_execsql_test 5.3.1 { SELECT * FROM aux.sqlite_stat1  } {}
+do_execsql_test 5.3.2 { ANALYZE aux } {}
+do_execsql_test 5.3.3 { SELECT * FROM aux.sqlite_stat1  } {t1 i1 {2 1}}
+do_execsql_test 5.3.4 { SELECT * FROM main.sqlite_stat1 } {}
+
+#-------------------------------------------------------------------------
+# Attempting to run ANALYZE when the required sqlite_statXX functions
+# are missing is an error (because it would modify the database schema).
+#
+reset_db
+do_execsql_test 5.4 {
+  CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
+  CREATE TABLE t2(a INTEGER PRIMARY KEY, b, c);
+  CREATE INDEX i1 ON t1(b);
+  INSERT INTO t1 VALUES(1, 2, 3), (4, 5, 6);
+}
+db close
+sqlite3 db test.db -shared-schema 1
+foreach {tn sql} {
+  1 { ANALYZE }
+  2 { ANALYZE t1 }
+  3 { ANALYZE i1 }
+  4 { ANALYZE main }
+  5 { ANALYZE main.t1 }
+  6 { ANALYZE main.i1 }
+} {
+  do_catchsql_test 5.4.$tn $sql {1 {attempt to modify read-only schema}}
+}
+
+#-------------------------------------------------------------------------
+#
+reset_db
+do_execsql_test 6.0 {
+  CREATE TABLE t1(a INTEGER PRIMARY KEY, b, c);
+  CREATE VIEW v1 AS SELECT * FROM t1;
+}
+db close
+forcecopy test.db test.db2
+sqlite3 db test.db -shared-schema 1
+execsql { ATTACH 'test.db2' AS aux }
+
+do_execsql_test 6.1 {
+  INSERT INTO main.t1(a) VALUES(1), (2), (3);
+  INSERT INTO aux.t1(a) VALUES(4), (5), (6);
+  CREATE TEMP TABLE t2(i,t);
+  INSERT INTO t2 VALUES(2, 'two'), (5, 'five');
+}
+
+do_execsql_test 6.2 {
+  SELECT t FROM t2 WHERE i IN (SELECT a FROM aux.t1)
+} {five}
+do_execsql_test 6.3 {
+  SELECT t FROM t2 WHERE i IN (SELECT a FROM aux.v1)
+} {five}
+
+#-------------------------------------------------------------------------
+#
+reset_db
+do_execsql_test 7.0 {
+  CREATE TABLE p1(a PRIMARY KEY, b);
+  CREATE TABLE p2(a PRIMARY KEY, b);
+  CREATE TABLE c1(x REFERENCES p1 ON UPDATE CASCADE ON DELETE CASCADE);
+}
+
+db close
+forcecopy test.db test.db2
+sqlite3 db test.db -shared-schema 1
+execsql { ATTACH 'test.db2' AS aux }
+
+do_execsql_test 7.1 {
+  INSERT INTO aux.p1 VALUES(1, 'one');
+  INSERT INTO aux.p1 VALUES(2, 'two');
+  PRAGMA foreign_keys = on;
+}
+
+do_execsql_test 7.2 {
+  INSERT INTO aux.c1 VALUES(2);
+}
+
+do_execsql_test 7.3.1 {
+  PRAGMA foreign_keys = off;
+  INSERT INTO main.p2 SELECT * FROM aux.p1;
+}
+do_execsql_test 7.3.2 {
+  SELECT * FROM main.p2;
+} {1 one 2 two}
+
+do_execsql_test 7.3.3 {
+  INSERT INTO aux.p2 VALUES(1, 2);
+}
+
+do_execsql_test 7.3.4 {
+  SELECT main.p2.a FROM main.p2, aux.p2;
+} {1 2}
+
+do_execsql_test 7.3.5 {
+  SELECT * FROM main.p2, aux.p2;
+} {1 one 1 2   2 two 1 2}
+
+do_execsql_test 7.4 {
+  SELECT count(*) FROM aux.p2;
+} {1}
+
+
+finish_test
+
+
@@ -0,0 +1,336 @@
+# 2017 August 9
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+#
+
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix reuse2
+
+ifcapable !sharedschema {
+  finish_test
+  return
+}
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(x INTEGER PRIMARY KEY, y UNIQUE, z);
+  CREATE INDEX i1 ON t1(z);
+  PRAGMA schema_version;
+} {2}
+
+do_test 1.2 {
+  catch { db close }
+  catch { db2 close }
+  sqlite3 db2 test.db -shared-schema 1
+  sqlite3 db  test.db -shared-schema 1
+} {}
+
+do_execsql_test -db db2 1.3.1 {
+  INSERT INTO t1 VALUES(1, 2, 3);
+}
+
+do_execsql_test -db db2 1.3.2 {
+  INSERT INTO t1 VALUES(4, 5, 6);
+}
+
+do_execsql_test 1.3.3 {
+  SELECT * FROM t1;
+} {1 2 3 4 5 6}
+
+#--------------------------------------------------------------------------
+reset_db
+ifcapable fts5 {
+  do_execsql_test 2.0 {
+    CREATE VIRTUAL TABLE ft USING fts5(c);
+    INSERT INTO ft VALUES('one two three');
+  }
+  db close
+  sqlite3 db test.db -shared-schema 1
+
+  do_execsql_test 2.1 {
+    SELECT * FROM ft
+  } {{one two three}}
+}
+
+#--------------------------------------------------------------------------
+reset_db
+do_execsql_test 3.0 {
+  CREATE TABLE t1(x INTEGER PRIMARY KEY, y UNIQUE, z);
+  CREATE INDEX i1 ON t1(z);
+  PRAGMA schema_version;
+} {2}
+
+do_test 3.1 {
+  sqlite3 db1 test.db -shared-schema 1
+  sqlite3 db2 test.db -shared-schema 1
+} {}
+
+do_execsql_test -db db1 3.2.1 { SELECT * FROM t1 }
+do_execsql_test -db db2 3.2.2 { SELECT * FROM t1 }
+
+register_schemapool_module db
+do_execsql_test 3.3 { 
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=2 nschema=1 ndelete=0}
+
+sqlite3 db3 test.db -shared-schema 1
+register_schemapool_module db3
+
+do_execsql_test 3.5 { 
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=2 nschema=1 ndelete=0}
+
+do_execsql_test -db db3 3.6 { 
+  SELECT * FROM t1;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=3 nschema=1 ndelete=0}
+
+do_execsql_test 3.7 { 
+  CREATE TABLE t2(x);
+}
+
+do_execsql_test 3.8 { 
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=3 nschema=1 ndelete=0}
+
+do_execsql_test -db db1 3.9.1 { SELECT * FROM t1 }
+do_execsql_test 3.9.2 { 
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=1 nschema=1 ndelete=0 nref=2 nschema=1 ndelete=0}
+
+do_execsql_test -db db2 3.10.1 { SELECT * FROM t1 }
+do_execsql_test 3.10.2 { 
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool ORDER BY 1;
+} {nref=1 nschema=1 ndelete=0 nref=2 nschema=1 ndelete=0}
+
+do_execsql_test -db db3 3.11.1 { SELECT * FROM t1 }
+do_execsql_test 3.11.2 { 
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=3 nschema=1 ndelete=0}
+
+#--------------------------------------------------------------------------
+catch {db1 close}
+catch {db2 close}
+catch {db3 close}
+reset_db
+do_execsql_test 4.0.1 {
+  CREATE TABLE x1(a, b, c);
+  CREATE INDEX x1a ON x1(a);
+  CREATE INDEX x1b ON x1(b);
+}
+do_test 4.0.2 {
+  db close
+  for {set i 1} {$i < 6} {incr i} {
+    forcedelete test.db${i}-journal test.db${i}-wal test.db${i}-wal2 
+    forcecopy test.db test.db${i}
+  }
+  sqlite3 db  test.db
+  sqlite3 db2 test.db -shared-schema 1
+} {}
+
+register_schemapool_module db
+do_execsql_test 4.0.3 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {}
+
+do_test 4.1.1 {
+  execsql { 
+    ATTACH 'test.db1' AS db1; 
+    ATTACH 'test.db2' AS db2;
+    ATTACH 'test.db3' AS db3;
+    ATTACH 'test.db4' AS db4;
+    ATTACH 'test.db5' AS db5;
+  } db2
+} {}
+do_execsql_test 4.1.2 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {}
+do_execsql_test -db db2 4.1.3 {
+  SELECT * FROM db3.x1
+}
+do_execsql_test 4.1.4 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=1 nschema=1 ndelete=0}
+do_execsql_test -db db2 4.1.5 {
+  SELECT * FROM db2.x1
+}
+do_execsql_test 4.1.6 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=2 nschema=1 ndelete=0}
+do_execsql_test -db db2 4.1.7 {
+  SELECT * FROM x1
+}
+do_execsql_test 4.1.8 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=6 nschema=1 ndelete=0}
+
+do_test 4.2.1 {
+  catchsql { SELECT * FROM abc } db2
+} {1 {no such table: abc}}
+do_execsql_test 4.2.2 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=6 nschema=1 ndelete=0}
+
+register_schemapool_module db2
+do_execsql_test -db db2 4.3.1 {
+  INSERT INTO x1 VALUES(1, 2, 3);
+  INSERT INTO db1.x1 VALUES(4, 5, 6);
+  INSERT INTO db2.x1 VALUES(7, 8, 9);
+  INSERT INTO db3.x1 VALUES(10, 11, 12);
+  INSERT INTO db4.x1 VALUES(13, 14, 15);
+  INSERT INTO db5.x1 VALUES(16, 17, 18);
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=6 nschema=1 ndelete=0}
+
+do_execsql_test -db db2 4.3.2 {
+  SELECT * FROM db5.x1;
+  SELECT * FROM db4.x1;
+  SELECT * FROM db3.x1;
+  SELECT * FROM db2.x1;
+  SELECT * FROM db1.x1;
+  SELECT * FROM x1;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {
+  16 17 18  13 14 15  10 11 12  7 8 9  4 5 6  1 2 3
+  nref=6 nschema=1 ndelete=0
+}
+
+do_execsql_test -db db2 4.3.3 {
+  UPDATE x1 SET a=a+10;
+  UPDATE db5.x1 SET a=a+10;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {
+  nref=6 nschema=1 ndelete=0
+}
+
+do_execsql_test -db db2 4.3.4 {
+  SELECT * FROM db5.x1;
+  SELECT * FROM db4.x1;
+  SELECT * FROM db3.x1;
+  SELECT * FROM db2.x1;
+  SELECT * FROM db1.x1;
+  SELECT * FROM x1;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {
+  26 17 18  13 14 15  10 11 12  7 8 9  4 5 6  11 2 3
+  nref=6 nschema=1 ndelete=0
+}
+
+do_execsql_test -db db2 4.3.5 {
+  DELETE FROM db3.x1;
+  DELETE FROM x1;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {
+  nref=6 nschema=1 ndelete=0
+}
+
+do_execsql_test -db db2 4.3.6 {
+  SELECT * FROM db5.x1;
+  SELECT * FROM db4.x1;
+  SELECT * FROM db3.x1;
+  SELECT * FROM db2.x1;
+  SELECT * FROM db1.x1;
+  SELECT * FROM x1;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {
+  26 17 18  13 14 15  7 8 9  4 5 6 
+  nref=6 nschema=1 ndelete=0
+}
+
+do_execsql_test -db db2 4.3.6 {
+  SELECT * FROM db5.x1, db4.x1, db1.x1;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {26 17 18 13 14 15 4 5 6 nref=6 nschema=3 ndelete=0}
+
+#--------------------------------------------------------------------------
+# Test the incremental-blob API with REUSE_SCHEMA connections.
+#
+catch {db1 close}
+catch {db2 close}
+catch {db3 close}
+reset_db
+do_execsql_test 5.0.1 {
+  CREATE TABLE bbb(a INTEGER PRIMARY KEY, b);
+}
+db close
+do_test 5.0.2 {
+  sqlite3 db2 test.db -shared-schema 1
+  register_schemapool_module db2
+  for {set i 1} {$i<6} {incr i} {
+    forcedelete test.db${i}-journal test.db${i}-wal test.db${i}-wal2 
+    forcecopy test.db test.db${i}
+    sqlite3 db test.db${i}
+    db eval { INSERT INTO bbb VALUES(123, 'database_' || $i) }
+    db close
+    db2 eval "ATTACH 'test.db${i}' AS db${i}"
+  }
+  execsql {
+    SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+      FROM schemapool;
+  } db2
+} {nref=6 nschema=1 ndelete=0}
+
+do_test 5.1.1 {
+  set res [list]
+  for {set i 1} {$i<6} {incr i} {
+    set chan [db2 incrblob db${i} bbb b 123]
+    lappend res [gets $chan]
+    close $chan
+  }
+  set res
+} {database_1 database_2 database_3 database_4 database_5}
+
+do_execsql_test -db db2 5.1.2 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=6 nschema=1 ndelete=0}
+
+do_test 5.2.1 {
+  sqlite3_table_column_metadata db2 main bbb a
+} {INTEGER BINARY 0 1 0}
+do_test 5.2.2 {
+  sqlite3_table_column_metadata db2 main bbb b
+} {{} BINARY 0 0 0}
+
+do_execsql_test -db db2 5.2.3 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {nref=6 nschema=1 ndelete=0}
+
+do_execsql_test -db db2 5.2.4 {
+  PRAGMA integrity_check;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete
+  FROM schemapool;
+} {ok nref=6 nschema=1 ndelete=5}
+
+finish_test
+
@@ -0,0 +1,355 @@
+# 2019 February 12
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+#
+
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix reuse3
+
+ifcapable !sharedschema {
+  finish_test
+  return
+}
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(x INTEGER PRIMARY KEY, y UNIQUE, z);
+  CREATE INDEX i1 ON t1(z);
+  CREATE TABLE t2(a);
+} {}
+
+db close
+sqlite3 db test.db -shared-schema 1
+
+do_execsql_test 1.1 {
+  CREATE TEMP VIEW v1 AS SELECT * FROM t1;
+  SELECT * FROM v1;
+}
+
+do_execsql_test 1.2 {
+  CREATE TEMP TRIGGER tr1 AFTER INSERT ON t1 BEGIN
+    INSERT INTO t2 VALUES(new.x);
+  END;
+}
+
+do_execsql_test 1.3 {
+  INSERT INTO t1 VALUES(1, 2, 3);
+}
+
+do_execsql_test 1.4 {
+  SELECT * FROM t2
+} {1}
+
+do_execsql_test 1.5 {
+  SELECT * FROM v1
+} {1 2 3}
+
+do_execsql_test 1.6 {
+  BEGIN;
+    DROP TRIGGER tr1;
+  ROLLBACK;
+}
+
+do_execsql_test 1.7 {
+  SELECT * FROM v1
+} {1 2 3}
+
+do_execsql_test 1.8 {
+  INSERT INTO t1 VALUES(4, 5, 6);
+  SELECT * FROM t2
+} {1 4}
+
+do_execsql_test 1.9 {
+  SELECT * FROM v1
+} {1 2 3 4 5 6}
+
+#-------------------------------------------------------------------------
+# Test error messages when parsing the schema with a REUSE_SCHEMA 
+# connection.
+reset_db
+do_execsql_test 2.0 {
+  CREATE TABLE x1(a, b, c);
+  CREATE TABLE y1(d, e, f);
+  PRAGMA writable_schema = 1;
+  UPDATE sqlite_master SET sql = 'CREATE TBL y1(d, e, f)' WHERE name = 'y1';
+}
+db close
+
+sqlite3 db test.db -shared-schema 1
+do_catchsql_test 2.1 {
+  SELECT * FROM x1;
+} {1 {malformed database schema (y1) - near "TBL": syntax error}}
+
+do_catchsql_test 2.2 {
+  SELECT * FROM x1;
+} {1 {malformed database schema (y1) - near "TBL": syntax error}}
+
+#-------------------------------------------------------------------------
+reset_db
+do_execsql_test 3.0 {
+  CREATE TABLE x1(a, b, c);
+  CREATE INDEX i1 ON x1(a, b, c);
+  CREATE TRIGGER tr1 AFTER INSERT ON x1 BEGIN
+    SELECT 1, 2, 3, 4, 5;
+  END;
+  INSERT INTO x1 VALUES(1, 2, 3);
+}
+sqlite3 db1 test.db -shared-schema 1
+
+do_test 3.1 {
+  execsql { SELECT * FROM x1 } db1
+  set N [lindex [sqlite3_db_status db1 SCHEMA_USED 0] 1]
+  expr $N==$N
+} 1
+
+sqlite3 db2 test.db -shared-schema 1
+do_test 3.2 {
+  execsql { SELECT * FROM x1 } db2
+  set N2 [lindex [sqlite3_db_status db2 SCHEMA_USED 0] 1]
+  expr $N2>($N/2) && $N2<($N/2)+400
+} 1
+
+sqlite3 db3 test.db -shared-schema 1
+sqlite3 db4 test.db -shared-schema 1
+do_test 3.3 {
+  execsql { SELECT * FROM x1 } db3
+  execsql { SELECT * FROM x1 } db4
+  set N4 [lindex [sqlite3_db_status db2 SCHEMA_USED 0] 1]
+  set M [expr 2*($N-$N2)]
+  set {} {}
+} {}
+do_test 3.3.1 { expr {(($M / 4) + $N-$M)} } "#/$N4/"
+
+catch { db1 close }
+catch { db2 close }
+catch { db3 close }
+catch { db4 close }
+
+#-------------------------------------------------------------------------
+# 4.1 Test the REINDEX command.
+# 4.2 Test CREATE TEMP ... commands.
+#
+reset_db
+do_execsql_test 4.1.0 {
+  CREATE TABLE x1(a, b, c);
+  CREATE INDEX x1a ON x1(a);
+  CREATE INDEX x1b ON x1(b);
+  CREATE INDEX x1c ON x1(c);
+}
+db close
+sqlite3 db test.db -shared-schema 1
+
+do_execsql_test 4.1.1 {
+  REINDEX x1;
+  REINDEX x1a;
+  REINDEX x1b;
+  REINDEX x1c;
+  REINDEX;
+}
+
+do_test 4.1.2 {
+  for {set i 1} {$i < 5} {incr i} {
+    forcedelete test.db${i} test.db${i}-wal test.db${i}-journal
+    forcecopy test.db test.db${i}
+    execsql "ATTACH 'test.db${i}' AS db${i}"
+  }
+  register_schemapool_module db
+  set {} {}
+  execsql { 
+    SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool 
+  }
+} {nref=5 nschema=1 ndelete=0}
+
+do_execsql_test 4.1.3 {
+  REINDEX  x1;
+  REINDEX  x1a;
+  REINDEX  x1b;
+  REINDEX  x1c;
+  REINDEX  db1.x1a;
+  REINDEX  db2.x1b;
+  REINDEX  db3.x1c;
+}
+
+do_execsql_test 4.1.4 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool 
+} {nref=5 nschema=1 ndelete=28}
+
+#-------------------------------------------------------------------------
+db close
+sqlite3 db test.db -shared-schema 1
+register_schemapool_module db
+do_execsql_test 4.2.0 {
+  ATTACH 'test.db1' AS db1;
+  ATTACH 'test.db2' AS db2;
+  ATTACH 'test.db3' AS db3;
+  ATTACH 'test.db4' AS db4;
+
+  SELECT * FROM db1.x1;
+  SELECT * FROM db2.x1;
+  SELECT * FROM db3.x1;
+  SELECT * FROM db4.x1;
+}
+
+do_execsql_test 4.2.1 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool; 
+} {nref=5 nschema=1 ndelete=0}
+
+do_execsql_test 4.2.2 {
+  CREATE TEMP TABLE t1(a, b, c);
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool; 
+} {nref=5 nschema=1 ndelete=0}
+
+do_execsql_test 4.2.3 {
+  CREATE INDEX t1a ON t1(a);
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool; 
+} {nref=5 nschema=1 ndelete=0}
+
+do_execsql_test 4.2.4 {
+  CREATE TRIGGER tr1 AFTER INSERT ON t1 BEGIN
+    SELECT 1,2,3,4;
+  END;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool; 
+} {nref=5 nschema=1 ndelete=0}
+
+do_execsql_test 4.2.5 {
+  DROP TABLE t1;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool; 
+} {nref=5 nschema=1 ndelete=0}
+
+do_execsql_test 4.2.6 {
+  CREATE TEMP TRIGGER tr1 AFTER INSERT ON db2.x1 BEGIN
+    SELECT 1,2,3,4;
+  END;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool; 
+} {nref=5 nschema=1 ndelete=0}
+
+do_execsql_test 4.2.7 {
+  DROP TRIGGER tr1;
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema, 'ndelete=' || nDelete 
+    FROM schemapool; 
+} {nref=5 nschema=1 ndelete=4}
+
+#--------------------------------------------------------------------------
+reset_db
+do_execsql_test 5.0 {
+  CREATE TABLE t1(a, b);
+  CREATE TABLE t2(a, b);
+  CREATE TABLE t3(a, b);
+}
+
+sqlite3 db2 test.db -shared-schema 1
+register_schemapool_module db2
+
+do_execsql_test 5.1 {
+  PRAGMA writable_schema = 1;
+  UPDATE sqlite_master SET sql='CREATE TABLE t3 a,b' WHERE name = 't3';
+}
+
+do_test 5.2 { 
+  catchsql { SELECT * FROM t1 } db2
+} {1 {malformed database schema (t3) - near "a": syntax error}}
+
+do_test 5.3 { 
+  catchsql { SELECT nref,nschema FROM schemapool } db2
+} {1 {vtable constructor failed: schemapool}}
+
+do_execsql_test 5.4 {
+  PRAGMA writable_schema = 1;
+  UPDATE sqlite_master SET sql='CREATE TABLE t3(a,b)' WHERE name = 't3';
+}
+
+do_test 5.5 { 
+  catchsql { SELECT nref,nschema FROM schemapool } db2
+} {0 {1 1}}
+
+db2 close
+db close
+do_test 5.6.1 {
+  forcedelete test.db2 test.db2-wal test.db2-journal
+  forcecopy test.db test.db2
+  sqlite3 db test.db
+  sqlite3 db2 test.db  -shared-schema 1
+  sqlite3 db3 test.db2 -shared-schema 1
+  register_schemapool_module db
+} {}
+
+do_execsql_test -db db2 5.6.2 { SELECT * FROM t1 }
+do_execsql_test -db db3 5.6.3 { SELECT * FROM t1 }
+do_execsql_test 5.6.4 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool; 
+  CREATE TABLE t4(x);
+  DROP TABLE t4;
+} {nref=2 nschema=1}
+do_execsql_test -db db2 5.6.5 { SELECT * FROM t1 }
+do_execsql_test -db db3 5.6.6 { SELECT * FROM t1 }
+do_execsql_test 5.6.7 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool; 
+  ATTACH 'test.db2' AS db2;
+  CREATE TABLE db2.t4(x);
+  DROP TABLE db2.t4;
+} {nref=1 nschema=1 nref=1 nschema=1}
+do_execsql_test -db db2 5.6.8 { SELECT * FROM t1 }
+do_execsql_test -db db3 5.6.9 { SELECT * FROM t1 }
+do_execsql_test 5.6.10 {
+  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool; 
+} {nref=2 nschema=1}
+
+#-------------------------------------------------------------------------
+reset_db
+do_execsql_test 6.0 {
+  CREATE TABLE t1(a, b);
+  CREATE TABLE t2(a, b);
+  CREATE TABLE t3(a, b);
+}
+
+do_test 6.1 {
+  db close
+  sqlite3 db test.db -shared-schema 1
+  for {set i 1} {$i < 5} {incr i} {
+    set base "test.db$i"
+    set nm "aux$i"
+    forcedelete $base $base-wal $base-journal
+    forcecopy test.db $base
+    execsql "ATTACH '$base' AS $nm"
+  }
+} {}
+
+do_test 6.2 {
+  set N1 [lindex [sqlite3_db_status db SCHEMA_USED 0] 1]
+  set N2 [lindex [sqlite3_db_status db SCHEMA_USED 0] 1]
+  expr ($N1==0 && $N2==0)
+} {1}
+
+do_test 6.3 {
+  execsql { SELECT * FROM main.t1 }
+  set N1 [lindex [sqlite3_db_status db SCHEMA_USED 0] 1]
+  set N2 [lindex [sqlite3_db_status db SCHEMA_USED 0] 1]
+  expr {$N1>0 && $N2>0 && $N1==$N2}
+} {1}
+
+do_test 6.4 {
+  execsql { SELECT * FROM aux1.t1 }
+  set N3 [lindex [sqlite3_db_status db SCHEMA_USED 0] 1]
+  set N4 [lindex [sqlite3_db_status db SCHEMA_USED 0] 1]
+  list $N3 $N4
+} "#/$N1 $N1/"
+
+finish_test
+
@@ -0,0 +1,173 @@
+# 2019 February 12
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix reuse4
+
+ifcapable !sharedschema {
+  finish_test
+  return
+}
+
+foreach {tn sharedschema} {
+  1 0  
+  2 1  
+} {
+  reset_db
+
+  do_execsql_test 1.$tn.0 {
+    CREATE TABLE x1(a, b);
+    CREATE INDEX x1a ON x1(a);
+    CREATE INDEX x1b ON x1(b);
+    CREATE TABLE x2(a, b);
+  }
+  db close
+  
+  do_test 1.$tn.1 {
+    for {set i 1} {$i<4} {incr i} {
+      forcedelete test.db$i test.db$i-journal test.db$i-wal
+      forcecopy test.db test.db$i
+    }
+  
+    sqlite3 db test.db -shared-schema $sharedschema
+    for {set i 1} {$i<4} {incr i} {
+      execsql " ATTACH 'test.db$i' AS db$i "
+    }
+  } {}
+  
+  do_execsql_test 1.$tn.2 {
+    WITH s(i) AS ( SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<10 )
+    INSERT INTO x1 SELECT i, i FROM s;
+  
+    INSERT INTO db3.x2 SELECT * FROM x1;
+    INSERT INTO db2.x1 SELECT * FROM db3.x2;
+    CREATE TEMP TRIGGER tr1 AFTER INSERT ON db2.x2 BEGIN
+      INSERT INTO x1 VALUES(new.a, new.b);
+    END;
+    INSERT INTO db2.x2 SELECT * FROM x1 WHERE a%2;
+    DELETE FROM x1 WHERE a<3;
+    INSERT INTO db3.x1 SELECT * FROM db2.x2;
+  
+    DETACH db3;
+    ATTACH 'test.db3' AS db3;
+  
+    UPDATE db3.x1 SET a=a-10 WHERE b NOT IN (SELECT b FROM db2.x2);
+  
+    CREATE TEMP TABLE x1(a, b);
+    INSERT INTO db2.x2 VALUES(50, 60), (60, 70), (80, 90);
+    ALTER TABLE x1 RENAME TO x2;
+    ALTER TABLE x2 ADD COLUMN c;
+    ALTER TABLE x2 RENAME a TO aaa;
+    DELETE FROM x1 WHERE b>8;
+    UPDATE db3.x2 SET b=b*10;
+  
+    BEGIN;
+      CREATE TEMP TABLE x5(x);
+      INSERT INTO x5 VALUES(1);
+    ROLLBACK;
+  
+    INSERT INTO main.x2 VALUES(123, 456);
+  }
+  
+  integrity_check 1.$tn.3
+  
+  do_execsql_test 1.$tn.4 {
+    SELECT * FROM main.x1; SELECT 'xxx';
+    SELECT * FROM main.x2; SELECT 'xxx';
+    SELECT * FROM temp.x2; SELECT 'xxx';
+  
+    SELECT * FROM db1.x1; SELECT 'xxx';
+    SELECT * FROM db1.x2; SELECT 'xxx';
+    SELECT * FROM db2.x1; SELECT 'xxx';
+    SELECT * FROM db2.x2; SELECT 'xxx';
+    SELECT * FROM db3.x1; SELECT 'xxx';
+    SELECT * FROM db3.x2; SELECT 'xxx';
+  } {
+    3 3 4 4 5 5 6 6 7 7 8 8 3 3 5 5 7 7 xxx 
+    123 456 xxx 
+    50 60 {} 60 70 {} 80 90 {} xxx
+    xxx
+    xxx
+    1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 xxx
+    1 1 3 3 5 5 7 7 9 9 50 60 60 70 80 90 xxx
+    1 1 3 3  5 5 7 7 9 9 xxx 
+    1 10 2 20 3 30 4 40 5 50 6 60 7 70 8 80 9 90 10 100 xxx
+  }
+  
+  do_test 1.$tn.5.1 {
+    sqlite3 db2 test.db
+    db2 eval { CREATE TABLE x3(x) }
+  } {}
+  do_execsql_test 1.$tn.5.2 {
+    SELECT * FROM main.x1; SELECT 'xxx';
+    SELECT * FROM main.x2; SELECT 'xxx';
+    SELECT * FROM main.x3; SELECT 'xxx';
+  } {
+    3 3 4 4 5 5 6 6 7 7 8 8 3 3 5 5 7 7 xxx 
+    123 456 xxx 
+    xxx
+  }
+}
+
+#-------------------------------------------------------------------------
+# Test some PRAGMA statements with shared-schema connections.
+#
+reset_db
+do_execsql_test 2.0 {
+  CREATE TABLE t1(a, b, c);
+  CREATE INDEX t1abc ON t1(a, b, c);
+}
+
+foreach {tn pragma nSchema nDelete} {
+  1 "PRAGMA synchronous = OFF"     1 0
+  2 "PRAGMA cache_size = 200"      1 0
+  3 "PRAGMA aux2.integrity_check"  1 0
+  4 "PRAGMA      integrity_check"  1 5
+  5 "PRAGMA index_info=t1abc"      1 5
+  6 "PRAGMA aux3.index_info=t1abc" 1 0
+  7 "PRAGMA journal_mode"          1 0
+  8 "PRAGMA aux2.wal_checkpoint"   1 0
+  9 "PRAGMA wal_checkpoint"        1 0
+} {
+  do_test 2.$tn.1 {
+    catch { db close }
+    catch { db2 close }
+    for {set i 1} {$i < 6} {incr i} {
+      forcedelete "test.db$i" "test.db${i}-wal" "test.db${i}-journal"
+      forcecopy test.db test.db$i
+    }
+    sqlite3 db2 test.db -shared-schema 1
+    for {set i 1} {$i < 6} {incr i} {
+      execsql "ATTACH 'test.db$i' AS aux$i" db2
+    }
+  } {}
+
+  sqlite3 db test.db
+  register_schemapool_module db
+
+  do_test 2.$tn.2 {
+    execsql $pragma db2
+    execsql { SELECT 'nschema='||nschema, 'ndelete='||nDelete FROM schemapool }
+  } "nschema=$nSchema ndelete=$nDelete"
+
+  do_test 2.$tn.3 {
+    execsql {
+      SELECT * FROM main.t1,aux1.t1,aux2.t1,aux3.t1,aux4.t1,aux5.t1
+    } db2
+    execsql { SELECT 'nschema=' || nschema, 'nref=' || nref FROM schemapool }
+  } "nschema=6 nref=6"
+}
+
+finish_test
+
@@ -0,0 +1,125 @@
+# 2019 February 26
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix reuse5
+set CLI [test_find_cli]
+
+ifcapable !sharedschema {
+  finish_test
+  return
+}
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(x, y);
+  CREATE TABLE t2(a, b, c);
+  CREATE INDEX t1x ON t1(x);
+  CREATE INDEX t1y ON t1(y);
+  CREATE VIEW v1 AS SELECT * FROM t2;
+}
+
+foreach {tn sql out1 out2} {
+  1 {
+    CREATE TABLE t1(x, y);
+    CREATE TABLE t2(a, b, c);
+    CREATE INDEX t1x ON t1(x);
+    CREATE INDEX t1y ON t1(y);
+    CREATE VIEW v1 AS SELECT * FROM t2;
+  } {
+    test.db2 is compatible
+  } {}
+
+  2 {
+    CREATE TABLE t1(x, y);
+    CREATE TABLE t2(a, b, c);
+    CREATE INDEX t1x ON t1(x);
+    CREATE INDEX t1y ON t1(y);
+    CREATE VIEW v1 AS SELECT * FROM t2;
+    CREATE TABLE x1(x);
+    DROP TABLE x1;
+  } {
+    test.db2 is NOT compatible (schema cookie)
+  } {
+    Fixing test.db2... test.db2 is compatible
+  }
+
+  3 {
+    CREATE TABLE t1(x, y);
+    CREATE TABLE t2(a, b, c);
+    CREATE INDEX t1y ON t1(y);
+    CREATE VIEW v1 AS SELECT * FROM t2;
+  } {
+    test.db2 is NOT compatible (objects)
+  } {}
+
+  4 {
+    CREATE TABLE t1(x, y);
+    CREATE TABLE t2(a, b, c);
+    CREATE INDEX t1x ON t1(X);
+    CREATE INDEX t1y ON t1(y);
+    CREATE VIEW v1 AS SELECT * FROM t2;
+  } {
+    test.db2 is NOT compatible (SQL)
+  } {}
+
+  5 {
+    CREATE TABLE t1(x, y);
+    CREATE TABLE t2(a, b, c);
+    CREATE INDEX t1y ON t1(y);
+    CREATE INDEX t1x ON t1(x);
+    CREATE VIEW v1 AS SELECT * FROM t2;
+  } {
+    test.db2 is NOT compatible (root pages)
+  } {
+    Fixing test.db2... test.db2 is compatible
+  }
+
+  6 {
+    CREATE TABLE t1(x, y);
+    CREATE TABLE t2(a, b, c);
+    CREATE INDEX t1x ON t1(x);
+    CREATE INDEX t1y ON t1(y);
+    CREATE VIEW v1 AS SELECT * FROM t2;
+    DROP INDEX t1x;
+    CREATE INDEX t1x ON t1(x);
+  } {
+    test.db2 is NOT compatible (order of sqlite_master rows)
+  } {
+    Fixing test.db2... test.db2 is compatible
+  }
+
+} {
+  forcedelete test.db2
+  sqlite3 db2 test.db2
+  db2 eval $sql
+  db2 close
+
+  if {$out2==""} {set out2 $out1}
+
+  do_test 1.$tn.1 {
+    catchcmd test.db ".shared-schema check test.db2"
+  } [list 0 [string trim $out1]]
+
+  do_test 1.$tn.2 {
+    catchcmd test.db ".shared-schema fix test.db2"
+  } [list 0 [string trim $out2]]
+
+  do_test 1.$tn.3 {
+    catchcmd test.db2 "PRAGMA integrity_check"
+  } [list 0 ok]
+}
+
+
+finish_test
+
@@ -0,0 +1,143 @@
+# 2019 February 26
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix reuse6
+
+ifcapable !sharedschema {
+  finish_test
+  return
+}
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(x, y);
+  CREATE TABLE t2(a, b, c);
+  CREATE INDEX t1x ON t1(x);
+  CREATE INDEX t1y ON t1(y);
+  CREATE VIEW v1 AS SELECT * FROM t2;
+
+  INSERT INTO t1 VALUES(1, 2), (3, 4), (5, 6);
+  INSERT INTO t2 VALUES('a', 'b', 'c'), ('d', 'e', 'f'), ('g', 'h', 'i');
+
+  ATTACH 'test.db2' AS aux;
+  CREATE TABLE t3(i, ii);
+  INSERT INTO t3 VALUES(10, 20);
+}
+
+sqlite3 db1 test.db -shared-schema 1
+sqlite3 db2 test.db -shared-schema 1
+
+do_execsql_test -db db1 1.1 {
+  ATTACH 'test.db2' AS aux;
+}
+
+do_test 1.2 {
+  execsql {SELECT * FROM t3} db1
+} {10 20}
+
+do_execsql_test -db db2 1.3 {
+  ATTACH 'test.db2' AS aux;
+}
+
+do_test 1.3 {
+  execsql {SELECT * FROM t3} db1
+} {10 20}
+
+do_execsql_test -db db2 1.5 {
+  SELECT * FROM t3;
+} {10 20}
+
+do_test 1.6 {
+  execsql {SELECT * FROM t3} db1
+} {10 20}
+
+db1 close
+db2 close
+
+#-------------------------------------------------------------------------
+reset_db
+forcedelete test.db2
+forcedelete test.db3
+do_execsql_test 2.0 {
+  CREATE TABLE t1(x, y);
+  ATTACH 'test.db2' AS aux2;
+  CREATE TABLE aux2.t2(x, y);
+  ATTACH 'test.db3' AS aux3;
+  CREATE TABLE aux3.t3(x, y);
+}
+
+sqlite3 db1 test.db -shared-schema 1
+do_execsql_test -db db1 2.1 {
+  ATTACH 'test.db2' AS aux2;
+  ATTACH 'test.db3' AS aux3;
+}
+
+do_test 2.2.1 {
+  catchsql { SELECT * FROM aux2.nosuchtable } db1
+} {1 {no such table: aux2.nosuchtable}}
+do_test 2.2.2 {
+  sqlite3_errcode db1
+} {SQLITE_ERROR}
+db1 close
+
+#-------------------------------------------------------------------------
+reset_db
+forcedelete test.db2
+ifcapable fts5 {
+  do_execsql_test 3.0 {
+    CREATE VIRTUAL TABLE ft USING fts5(a, b);
+    ATTACH 'test.db2' AS aux;
+    CREATE TABLE aux.t1(x, y, z);
+  }
+
+  sqlite3 db1 test.db -shared-schema 1
+  do_execsql_test -db db1 3.1 {
+    ATTACH 'test.db2' AS aux;
+  }
+
+  do_execsql_test -db db1 3.2 {
+    SELECT * FROM main.ft, aux.t1;
+  }
+  db1 close
+}
+
+#-------------------------------------------------------------------------
+reset_db
+forcedelete test.db2
+ifcapable fts5 {
+  do_execsql_test 4.0 {
+    CREATE VIRTUAL TABLE ft USING fts5(a, b);
+  }
+  forcecopy test.db test.db2
+
+  sqlite3 db1 test.db -shared-schema 1
+  do_execsql_test -db db1 4.1 {
+    ATTACH 'test.db2' AS aux;
+    SELECT * FROM main.ft;
+    SELECT * FROM aux.ft;
+  }
+
+  do_execsql_test -db db1 4.2 {
+    SELECT * FROM main.ft, aux.ft
+  }
+}
+
+
+
+
+
+
+
+finish_test
+
@@ -0,0 +1,54 @@
+# 2019 February 12
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+#
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix reusefault
+
+ifcapable !sharedschema {
+  finish_test
+  return
+}
+
+do_execsql_test 1.0 {
+  PRAGMA cache_size = 10;
+  CREATE TABLE t1(a UNIQUE, b UNIQUE);
+  INSERT INTO t1 VALUES(1, 2), (3, 4);
+}
+faultsim_save_and_close
+
+do_faultsim_test 1.1 -prep {
+  faultsim_restore
+  sqlite3 db test.db -shared-schema 1
+} -body {
+  execsql { SELECT * FROM t1 }
+} -test {
+  faultsim_test_result {0 {1 2 3 4}}
+}
+
+do_faultsim_test 1.2 -prep {
+  faultsim_restore
+  sqlite3 db test.db -shared-schema 1
+  execsql { SELECT * FROM t1 }
+  sqlite3 db2 test.db
+  db2 eval {CREATE TABLE a(a)}
+  db2 close
+} -body {
+  execsql { SELECT  * FROM t1 }
+} -test {
+  faultsim_test_result {0 {1 2 3 4}}
+}
+
+
+finish_test
+
@@ -26,6 +26,9 @@ set testprefix tcl
 # Check the error messages generated by tclsqlite
 #
 set r "sqlite_orig HANDLE ?FILENAME? ?-vfs VFSNAME? ?-readonly BOOLEAN? ?-create BOOLEAN? ?-nofollow BOOLEAN? ?-nomutex BOOLEAN? ?-fullmutex BOOLEAN? ?-uri BOOLEAN?"
+ifcapable sharedschema {
+  append r " ?-shared-schema BOOLEAN?"
+}
 if {[sqlite3 -has-codec]} {
  append r " ?-key CODECKEY?"
 }
@@ -38,7 +38,7 @@
 #define SEL(e) ((e)->iLine = ((e)->rc ? (e)->iLine : __LINE__))

 /* Database functions */
-#define opendb(w,x,y,z)         (SEL(w), opendb_x(w,x,y,z))
+#define opendb(w,x,y,z,f)       (SEL(w), opendb_x(w,x,y,z,f))
 #define closedb(y,z)            (SEL(y), closedb_x(y,z))

 /* Functions to execute SQL */
@@ -520,11 +520,14 @@ static void opendb_x(
  Error *pErr,                    /* IN/OUT: Error code */
  Sqlite *pDb,                    /* OUT: Database handle */
  const char *zFile,              /* Database file name */
-  int bDelete                     /* True to delete db file before opening */
+  int bDelete,                    /* True to delete db file before opening */
+  int flags
 ){
  if( pErr->rc==SQLITE_OK ){
    int rc;
-    int flags = SQLITE_OPEN_CREATE | SQLITE_OPEN_READWRITE | SQLITE_OPEN_URI;
+    if( flags==0 ){
+      flags = SQLITE_OPEN_CREATE | SQLITE_OPEN_READWRITE | SQLITE_OPEN_URI;
+    }
    if( bDelete ) unlink(zFile);
    rc = sqlite3_open_v2(zFile, &pDb->db, flags, 0);
    if( rc ){
@@ -926,7 +929,7 @@ static char *walthread1_thread(int iTid, void *pArg){
  Sqlite db = {0};                /* SQLite database connection */
  int nIter = 0;                  /* Iterations so far */

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    const char *azSql[] = {
      "SELECT md5sum(x) FROM t1 WHERE rowid != (SELECT max(rowid) FROM t1)",
@@ -965,7 +968,7 @@ static char *walthread1_ckpt_thread(int iTid, void *pArg){
  Sqlite db = {0};                /* SQLite database connection */
  int nCkpt = 0;                  /* Checkpoints so far */

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    usleep(500*1000);
    execsql(&err, &db, "PRAGMA wal_checkpoint");
@@ -984,7 +987,7 @@ static void walthread1(int nMs){
  Threadset threads = {0};        /* Test threads */
  int i;                          /* Iterator variable */

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db,
      "PRAGMA journal_mode = WAL;"
      "CREATE TABLE t1(x PRIMARY KEY);"
@@ -1017,7 +1020,7 @@ static char *walthread2_thread(int iTid, void *pArg){
    int journal_exists = 0;
    int wal_exists = 0;

-    opendb(&err, &db, "test.db", 0);
+    opendb(&err, &db, "test.db", 0, 0);

    sql_script(&err, &db, zJournal);
    clear_error(&err, SQLITE_BUSY);
@@ -1047,7 +1050,7 @@ static void walthread2(int nMs){
  Sqlite db = {0};
  Threadset threads = {0};

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, "CREATE TABLE t1(x INTEGER PRIMARY KEY, y UNIQUE)");
  closedb(&err, &db);

@@ -1067,7 +1070,7 @@ static char *walthread3_thread(int iTid, void *pArg){
  i64 iNextWrite;                 /* Next value this thread will write */
  int iArg = PTR2INT(pArg);

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  sql_script(&err, &db, "PRAGMA wal_autocheckpoint = 10");

  iNextWrite = iArg+1;
@@ -1104,7 +1107,7 @@ static void walthread3(int nMs){
  Threadset threads = {0};
  int i;

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, 
      "PRAGMA journal_mode = WAL;"
      "CREATE TABLE t1(cnt PRIMARY KEY, sum1, sum2);"
@@ -1127,7 +1130,7 @@ static char *walthread4_reader_thread(int iTid, void *pArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    integrity_check(&err, &db);
  }
@@ -1142,7 +1145,7 @@ static char *walthread4_writer_thread(int iTid, void *pArg){
  Sqlite db = {0};                /* SQLite database connection */
  i64 iRow = 1;

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  sql_script(&err, &db, "PRAGMA wal_autocheckpoint = 15;");
  while( !timetostop(&err) ){
    execsql_i64(
@@ -1162,7 +1165,7 @@ static void walthread4(int nMs){
  Sqlite db = {0};
  Threadset threads = {0};

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, 
      "PRAGMA journal_mode = WAL;"
      "CREATE TABLE t1(a INTEGER PRIMARY KEY, b UNIQUE);"
@@ -1182,7 +1185,7 @@ static char *walthread5_thread(int iTid, void *pArg){
  Sqlite db = {0};                /* SQLite database connection */
  i64 nRow;

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  nRow = execsql_i64(&err, &db, "SELECT count(*) FROM t1");
  closedb(&err, &db);

@@ -1195,7 +1198,7 @@ static void walthread5(int nMs){
  Sqlite db = {0};
  Threadset threads = {0};

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, 
      "PRAGMA wal_autocheckpoint = 0;"
      "PRAGMA page_size = 1024;"
@@ -1286,7 +1289,7 @@ static void cgt_pager_1(int nMs){
  Error err = {0};
  Sqlite db = {0};

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db,
      "PRAGMA cache_size = 2000;"
      "PRAGMA page_size = 1024;"
@@ -1315,7 +1318,7 @@ static char *dynamic_triggers_1(int iTid, void *pArg){
  int nDrop = 0;
  int nCreate = 0;

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    int i;

@@ -1368,7 +1371,7 @@ static char *dynamic_triggers_2(int iTid, void *pArg){
  int nInsert = 0;
  int nDelete = 0;

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    do {
      iVal = (iVal+1)%100;
@@ -1393,7 +1396,7 @@ static void dynamic_triggers(int nMs){
  Sqlite db = {0};
  Threadset threads = {0};

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, 
      "PRAGMA page_size = 1024;"
      "PRAGMA journal_mode = WAL;"
@@ -1433,6 +1436,7 @@ static void dynamic_triggers(int nMs){
 #include "tt3_lookaside1.c"
 #include "tt3_vacuum.c"
 #include "tt3_stress.c"
+#include "tt3_reuseschema.c"
 #include "tt3_shared.c"

 int main(int argc, char **argv){
@@ -1458,6 +1462,7 @@ int main(int argc, char **argv){
    { vacuum1,             "vacuum1", 10000 },
    { stress1,             "stress1", 10000 },
    { stress2,             "stress2", 60000 },
+    { reuse_schema_1,      "reuse_schema_1", 20000 },
    { shared1,             "shared1", 10000 },
  };
  static char *substArgv[] = { 0, "*", 0 };
@@ -70,7 +70,7 @@ static char *checkpoint_starvation_reader(int iTid, void *pArg){
  Error err = {0};
  Sqlite db = {0};

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    i64 iCount1, iCount2;
    sql_script(&err, &db, "BEGIN");
@@ -96,7 +96,7 @@ static void checkpoint_starvation_main(int nMs, CheckpointStarvationCtx *p){
  int nInsert = 0;
  int i;

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, 
      "PRAGMA page_size = 1024;"
      "PRAGMA journal_mode = WAL;"
@@ -19,7 +19,7 @@ static char *create_drop_index_thread(int iTid, void *pArg){
  Sqlite db = {0};                /* SQLite database connection */

  while( !timetostop(&err) ){
-    opendb(&err, &db, "test.db", 0);
+    opendb(&err, &db, "test.db", 0, 0);

    sql_script(&err, &db, 
      "DROP INDEX IF EXISTS i1;"
@@ -51,7 +51,7 @@ static void create_drop_index_1(int nMs){
  Sqlite db = {0};
  Threadset threads = {0};

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, 
     "CREATE TABLE t11(a, b, c, d);"
     "WITH data(x) AS (SELECT 1 UNION ALL SELECT x+1 FROM data WHERE x<100) "
@@ -22,7 +22,7 @@ static char *lookaside1_thread_reader(int iTid, void *pArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);

  while( !timetostop(&err) ){
    sqlite3_stmt *pStmt = 0;
@@ -47,7 +47,7 @@ static char *lookaside1_thread_writer(int iTid, void *pArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);

  do{
    sql_script(&err, &db, 
@@ -68,7 +68,7 @@ static void lookaside1(int nMs){
  Sqlite db = {0};
  Threadset threads = {0};

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, 
     "CREATE TABLE t1(x PRIMARY KEY) WITHOUT ROWID;"
     "WITH data(x,y) AS ("
@@ -0,0 +1,73 @@
+/*
+** 2014 December 9
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+**
+**     reuse_schema_1
+*/
+
+
+static char *reuse_schema_thread(int iTid, void *pArg){
+  Error err = {0};                /* Error code and message */
+  Sqlite db = {0};                /* SQLite database connection */
+  int iRep = 0;
+
+  while( !timetostop(&err) ){
+    int f = SQLITE_OPEN_READWRITE|SQLITE_OPEN_SHARED_SCHEMA;
+    opendb(&err, &db, "test.db", 0, f);
+
+    execsql_i64(&err, &db, "SELECT count(*) FROM t1");
+    sql_script(&err, &db, "ATTACH 'test.db2' AS aux");
+    execsql_i64(&err, &db, "SELECT count(*) FROM t1");
+
+    closedb(&err, &db);
+    iRep++;
+  }
+
+  print_and_free_err(&err);
+  return sqlite3_mprintf("%d", iRep);
+}
+
+static void reuse_schema_1(int nMs){
+  Error err = {0};
+  Sqlite db = {0};
+  Threadset threads = {0};
+
+  opendb(&err, &db, "test.db", 1, 0);
+  sql_script(&err, &db, 
+     "CREATE TABLE t1(a, b, c, d);"
+     "WITH data(x) AS (SELECT 1 UNION ALL SELECT x+1 FROM data WHERE x<100) "
+     "INSERT INTO t1 SELECT x,x,x,x FROM data;"
+  );
+  closedb(&err, &db);
+  opendb(&err, &db, "test.db2", 1, 0);
+  sql_script(&err, &db, 
+#ifdef SQLITE_ENABLE_FTS5
+     "CREATE VIRTUAL TABLE t2 USING fts5(a, b, c, d);"
+#else
+     "CREATE TABLE t2(a, b, c, d);"
+#endif
+     "WITH data(x) AS (SELECT 1 UNION ALL SELECT x+1 FROM data WHERE x<100) "
+     "INSERT INTO t2 SELECT x*2,x*2,x*2,x*2 FROM data;"
+  );
+  closedb(&err, &db);
+
+  setstoptime(&err, nMs);
+
+  launch_thread(&err, &threads, reuse_schema_thread, 0);
+  launch_thread(&err, &threads, reuse_schema_thread, 0);
+  launch_thread(&err, &threads, reuse_schema_thread, 0);
+  launch_thread(&err, &threads, reuse_schema_thread, 0);
+  launch_thread(&err, &threads, reuse_schema_thread, 0);
+
+  join_all_threads(&err, &threads);
+  sqlite3_enable_shared_cache(0);
+  print_and_free_err(&err);
+}
@@ -21,7 +21,7 @@ static char *stress_thread_1(int iTid, void *pArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    sql_script(&err, &db, "CREATE TABLE IF NOT EXISTS t1(a PRIMARY KEY, b)");
    clear_error(&err, SQLITE_LOCKED);
@@ -40,7 +40,7 @@ static char *stress_thread_2(int iTid, void *pArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */
  while( !timetostop(&err) ){
-    opendb(&err, &db, "test.db", 0);
+    opendb(&err, &db, "test.db", 0, 0);
    sql_script(&err, &db, "SELECT * FROM sqlite_schema;");
    clear_error(&err, SQLITE_LOCKED);
    closedb(&err, &db);
@@ -59,7 +59,7 @@ static char *stress_thread_3(int iTid, void *pArg){
  int i1 = 0;
  int i2 = 0;

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    sql_script(&err, &db, "SELECT * FROM t1 ORDER BY a;");
    i1++;
@@ -82,11 +82,11 @@ static char *stress_thread_4(int iTid, void *pArg){
  int i2 = 0;
  int iArg = PTR2INT(pArg);

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    if( iArg ){
      closedb(&err, &db);
-      opendb(&err, &db, "test.db", 0);
+      opendb(&err, &db, "test.db", 0, 0);
    }
    sql_script(&err, &db, 
        "WITH loop(i) AS (SELECT 1 UNION ALL SELECT i+1 FROM loop LIMIT 200) "
@@ -113,12 +113,12 @@ static char *stress_thread_5(int iTid, void *pArg){
  int i1 = 0;
  int i2 = 0;

-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  while( !timetostop(&err) ){
    i64 i = (i1 % 4);
    if( iArg ){
      closedb(&err, &db);
-      opendb(&err, &db, "test.db", 0);
+      opendb(&err, &db, "test.db", 0, 0);
    }
    execsql(&err, &db, "DELETE FROM t1 WHERE (rowid % 4)==:i", &i);
    i1++;
@@ -265,7 +265,7 @@ static char *stress2_workload19(int iTid, void *pArg){
  Sqlite db = {0};                /* SQLite database connection */
  const char *zDb = (const char*)pArg;
  while( !timetostop(&err) ){
-    opendb(&err, &db, zDb, 0);
+    opendb(&err, &db, zDb, 0, 0);
    sql_script(&err, &db, "SELECT * FROM sqlite_schema;");
    clear_error(&err, SQLITE_LOCKED);
    closedb(&err, &db);
@@ -290,7 +290,7 @@ static char *stress2_thread_wrapper(int iTid, void *pArg){

  while( !timetostop(&err) ){
    int cnt;
-    opendb(&err, &db, pCtx->zDb, 0);
+    opendb(&err, &db, pCtx->zDb, 0, 0);
    for(cnt=0; err.rc==SQLITE_OK && cnt<STRESS2_TABCNT; cnt++){
      pCtx->xProc(&err, &db, i1);
      i2 += (err.rc==SQLITE_OK);
@@ -342,7 +342,7 @@ static void stress2(int nMs){
  Threadset threads = {0};

  /* To make sure the db file is empty before commencing */
-  opendb(&err, &db, zDb, 1);
+  opendb(&err, &db, zDb, 1, 0);
  sql_script(&err, &db, 
      "CREATE TABLE IF NOT EXISTS t0(x PRIMARY KEY, y, z);"
      "CREATE INDEX IF NOT EXISTS i0 ON t0(y);"
@@ -23,7 +23,7 @@
 static char *vacuum1_thread_writer(int iTid, void *pArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */
-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);
  i64 i = 0;

  while( !timetostop(&err) ){
@@ -52,7 +52,7 @@ static char *vacuum1_thread_writer(int iTid, void *pArg){
 static char *vacuum1_thread_vacuumer(int iTid, void *pArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */
-  opendb(&err, &db, "test.db", 0);
+  opendb(&err, &db, "test.db", 0, 0);

  do{
    sql_script(&err, &db, "VACUUM");
@@ -69,7 +69,7 @@ static void vacuum1(int nMs){
  Sqlite db = {0};
  Threadset threads = {0};

-  opendb(&err, &db, "test.db", 1);
+  opendb(&err, &db, "test.db", 1, 0);
  sql_script(&err, &db, 
     "CREATE TABLE t1(x PRIMARY KEY, y BLOB);"
     "CREATE INDEX i1 ON t1(y);"
@@ -12,7 +12,7 @@

 # Flag meanings:
 set flagMeaning(NeedSchema) {Force schema load before running}
-set flagMeaning(ReadOnly)   {Read-only HEADER_VALUE}
+set flagMeaning(OneSchema)  {Only a single schema required}
 set flagMeaning(Result0)    {Acts as query when no argument}
 set flagMeaning(Result1)    {Acts as query when has one argument}
 set flagMeaning(SchemaReq)  {Schema required - "main" is default}
@@ -150,7 +150,7 @@ set pragma_def {
  ARG:  SQLITE_CellSizeCk

  NAME: default_cache_size
-  FLAG: NeedSchema Result0 SchemaReq NoColumns1
+  FLAG: NeedSchema Result0 SchemaReq NoColumns1 OneSchema
  COLS: cache_size
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS) && !defined(SQLITE_OMIT_DEPRECATED)

@@ -163,12 +163,12 @@ set pragma_def {
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: page_count
-  FLAG: NeedSchema Result0 SchemaReq
+  FLAG: NeedSchema Result0 SchemaReq OneSchema
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: max_page_count
  TYPE: PAGE_COUNT
-  FLAG: NeedSchema Result0 SchemaReq
+  FLAG: NeedSchema Result0 SchemaReq OneSchema
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: locking_mode
@@ -176,7 +176,7 @@ set pragma_def {
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: journal_mode
-  FLAG: NeedSchema Result0 SchemaReq
+  FLAG: NeedSchema Result0 SchemaReq OneSchema
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: journal_size_limit
@@ -184,18 +184,18 @@ set pragma_def {
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: cache_size
-  FLAG: NeedSchema Result0 SchemaReq NoColumns1
+  FLAG: NeedSchema Result0 SchemaReq NoColumns1 OneSchema
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: mmap_size
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: auto_vacuum
-  FLAG: NeedSchema Result0 SchemaReq NoColumns1
+  FLAG: NeedSchema Result0 SchemaReq NoColumns1 OneSchema
  IF:   !defined(SQLITE_OMIT_AUTOVACUUM)

  NAME: incremental_vacuum
-  FLAG: NeedSchema NoColumns
+  FLAG: NeedSchema NoColumns OneSchema
  IF:   !defined(SQLITE_OMIT_AUTOVACUUM)

  NAME: temp_store
@@ -215,7 +215,7 @@ set pragma_def {
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS) && SQLITE_ENABLE_LOCKING_STYLE

  NAME: synchronous
-  FLAG: NeedSchema Result0 SchemaReq NoColumns1
+  FLAG: NeedSchema Result0 SchemaReq NoColumns1 OneSchema
  IF:   !defined(SQLITE_OMIT_PAGER_PRAGMAS)

  NAME: table_info
@@ -232,7 +232,7 @@ set pragma_def {
  IF:   !defined(SQLITE_OMIT_SCHEMA_PRAGMAS)

  NAME: stats
-  FLAG: NeedSchema Result0 SchemaReq
+  FLAG: NeedSchema Result0 SchemaReq OneSchema
  COLS: tbl idx wdth hght flgs
  IF:   !defined(SQLITE_OMIT_SCHEMA_PRAGMAS) && defined(SQLITE_DEBUG)

@@ -256,7 +256,7 @@ set pragma_def {
  IF:   !defined(SQLITE_OMIT_SCHEMA_PRAGMAS)

  NAME: database_list
-  FLAG: NeedSchema Result0
+  FLAG: NeedSchema Result0 OneSchema
  COLS: seq name file
  IF:   !defined(SQLITE_OMIT_SCHEMA_PRAGMAS)

@@ -284,7 +284,7 @@ set pragma_def {
  IF:   !defined(SQLITE_OMIT_SCHEMA_PRAGMAS)

  NAME: foreign_key_list
-  FLAG: NeedSchema Result1 SchemaOpt
+  FLAG: NeedSchema Result1 SchemaOpt OneSchema
  COLS: id seq table from to on_update on_delete match
  IF:   !defined(SQLITE_OMIT_FOREIGN_KEY)

@@ -330,14 +330,14 @@ set pragma_def {

  NAME: data_version
  TYPE: HEADER_VALUE
-  ARG:  BTREE_DATA_VERSION
-  FLAG: ReadOnly Result0
+  ARG:  BTREE_DATA_VERSION|PRAGMA_HEADER_VALUE_READONLY
+  FLAG: Result0
  IF:   !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)

  NAME: freelist_count
  TYPE: HEADER_VALUE
-  ARG:  BTREE_FREE_PAGE_COUNT
-  FLAG: ReadOnly Result0
+  ARG:  BTREE_FREE_PAGE_COUNT|PRAGMA_HEADER_VALUE_READONLY
+  FLAG: Result0
  IF:   !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)

  NAME: application_id
@@ -351,7 +351,7 @@ set pragma_def {
  IF:   !defined(SQLITE_OMIT_COMPILEOPTION_DIAGS)

  NAME: wal_checkpoint
-  FLAG: NeedSchema
+  FLAG: NeedSchema OneSchema
  COLS: busy log checkpointed
  IF:   !defined(SQLITE_OMIT_WAL)

@@ -510,6 +510,12 @@ foreach f [lsort [array names allflags]] {
  set fv [expr {$fv*2}]
 }

+puts $fd "\n/* For PragTyp_HEADER_VALUE pragmas the Pragma.iArg value is set"
+puts $fd "** to the index of the header field to access (always 10 or less)."
+puts $fd "** Ored with HEADER_VALUE_READONLY if the field is read only. */"
+puts $fd "#define PRAGMA_HEADER_VALUE_READONLY 0x0100"
+puts $fd "#define PRAGMA_HEADER_VALUE_MASK 0x00FF\n"
+
 # Sort the column lists so that longer column lists occur first
 #
 proc colscmp {a b} {
Author	SHA1	Message	Date
drh	97d144ab61	Incorporate the 3.34.1 patches into the reuse-schema branch. FossilOrigin-Name: cc0e582854be11c29186d535130344c5486deb124ec4135a50ee1de21ea44a1d	2021-01-20 15:10:48 +00:00
drh	60405cd15c	Version 3.34.1 FossilOrigin-Name: 10e20c0b43500cfb9bbc0eaa061c57514f715d87238f4d835880cd846b9ebd1f	2021-01-20 14:10:07 +00:00
drh	b08dbd0f28	Fix an issue with sha3_query() when the first argument contains blank SQL statements. FossilOrigin-Name: a1a7a5f238fcfdcd56faba063e381258c9e2944d9b02b31d402a4207a607fc1c	2021-01-19 20:38:13 +00:00
drh	00a0b135ec	Bump the version number to 3.34.1. FossilOrigin-Name: cea7d0f8a3d9b3f5caae63ad555de25b53c577fc8e004127ec18cc7f0c6f1714	2021-01-19 20:17:46 +00:00
drh	90ab71bdc8	Fix a problem handling sub-queries with both a correlated WHERE clause and a "HAVING 0" clause where the parent query is itself an aggregate. The problem was apparently introduced by check-in [6e6b3729e0549de0] FossilOrigin-Name: 30a4c323650cc9498a6dacd1760dd5170d7cc7848c4e96ff6bd64da365f96366	2021-01-19 20:09:44 +00:00
drh	4dca7d4cfb	Prevent potential segfault in the sqlite-expert idxPopulateStat1 context cleanup code. FossilOrigin-Name: 69e31d52b2a7bde1ed72bc7b927ff451139fbc76504e750324e6368ad26b11b1	2021-01-19 20:04:37 +00:00
drh	1dc9cf947b	Fix a typo in the sqlite3_free_filename() documentation. FossilOrigin-Name: 7316ee19c590854545019a56799968143109929049424a8cc1dcf9624f98a544	2020-12-16 13:20:15 +00:00
dan	85aaf75855	Update this branch with latest trunk changes. FossilOrigin-Name: 846e8444f761a4f3e3e0fb89e87b329799a6e8dd32ac7580dc20eb6ff9ed0d36	2020-12-04 18:47:28 +00:00
drh	36b4ffef75	Merge the 3.34.0 release into the reuse-schema branch. FossilOrigin-Name: 73b5f614cd6603d6cf9605ac4ccb510a2560fca70a8a3f3f930cf2a4e853c301	2020-12-01 16:36:04 +00:00
dan	bd89471096	Merge trunk changes into this branch. FossilOrigin-Name: f4b7c10057a50c5b1f38d4e35ec684ad9d6e21278675fec98961e1fa408ded52	2020-11-25 20:29:45 +00:00
dan	5422f18381	Merge trunk changes into this branch. FossilOrigin-Name: 6004de525d90e5a32742349db9a7c818e1ae2d3bf3f57aff9058a3cb8f6f0fff	2020-11-18 21:15:42 +00:00
dan	934eb637c2	Merge latest trunk changes into this branch. FossilOrigin-Name: ae1a778dbbab2beb171678c55b82a0dc095b1515ae16059e199af510bcf89c03	2020-09-07 11:23:22 +00:00
dan	8280fcc66f	Merge tsan error fix from trunk into this branch. FossilOrigin-Name: 93cc60b34278ec45e382edbd99aa22268eb32bfe6c917bad7d1e9f158cedf57b	2020-09-04 19:12:16 +00:00
dan	5a5f8b366b	Update this branch with latest changes from trunk. FossilOrigin-Name: ca8deb44c70c3d8a1cdde5bb92a3db812e4e38bfce9a97feb658594c8267609f	2020-09-04 17:40:22 +00:00
drh	73d2d7938e	Merge the 3.33.0 release into the reuse-schema branch. FossilOrigin-Name: e456d437083c550570063b874d685f110162a0551f51d5f190f90c1354e6e996	2020-08-14 13:55:40 +00:00
drh	e805679133	Merge all changes since the 3.32.0 release into the reuse-schema branch. FossilOrigin-Name: b1a77b7eade14d58b3ccd50b98c2ffb6362d093f2cde2bd178ea62cef2cb8d9f	2020-08-11 14:55:17 +00:00
drh	bb85a9053e	Update the reuse-schema branch to version 3.32.1 FossilOrigin-Name: ecf8dece0362b79d248bae1847d2224d18af395c336a604bbcf2b29ffab645d5	2020-05-25 16:34:57 +00:00
drh	19b2d07824	Merge version 3.32.0 into the reuse-schema branch. FossilOrigin-Name: 31706878c3ab3ad8f84035553f0c4de25af1e371577e7caccba191fe172905ee	2020-05-22 18:41:15 +00:00
drh	02d30805c8	Bring the reuse-schema branch up to date with the latest trunk changes. FossilOrigin-Name: d8ea0cb69d9b47c2d3e1048671623cada18cc997612edf8f617ea48882e2b052	2020-05-18 19:11:35 +00:00
drh	6d78967393	Merge trunk enhancements in the reuse-schema branch. (Actual date of this check-in is 2020-05-18.) FossilOrigin-Name: 5af4abe98c747ff5c6a84b6cc1f7b69d9b492a807a8fd5234163f3bd9c96c574	2020-05-16 18:59:59 +00:00
dan	006f49bc9b	Merge trunk change [895bd20b29] into this branch. FossilOrigin-Name: 507f972e91ffdc8d80a6ce594139ea4c7afad38791a08032637340fbf49842bc	2020-03-05 18:59:59 +00:00
drh	0a6e45f4d9	Merge trunk enhancements into the reuse-schema branch. FossilOrigin-Name: 9d068e1ef04e84c025d2f696919dd5d1fe385abacbbd3ea31da58c74ae2812bf	2020-03-05 16:30:00 +00:00
dan	8e8c7ccc9b	Merge latest trunk changes into this branch. FossilOrigin-Name: 3f5650aae69498fce8c3f2b9c9e67e52f676776ea6d8a2f0f153fdeb8857231c	2020-02-27 15:20:37 +00:00
drh	c3c71c1451	Merge in version 3.31.0 FossilOrigin-Name: f418afa1bfde909bb90a60990e16be6beace9788319a5e1871e94b442fcd688c	2020-01-22 20:02:11 +00:00
drh	5e87610fdf	Merge recent fixes from trunk. FossilOrigin-Name: 9c920bbad3d0a79279e8ff89a01d0f197c77d0a530ac51c57e57fe6db316c905	2020-01-20 15:32:47 +00:00
dan	d3698b7fe8	Fix a couple of test case issues on this branch. FossilOrigin-Name: 9830a44bc65e1176ca11ae84d7a291e6986662d2bbac5e352ae6e2423358c60b	2020-01-18 19:58:06 +00:00
dan	72d2de6eef	Have this branch call sqlite3LockAndPrepare() instead of sqlite3Prepare() when parsing SQL for new schema objects in order to ensure that schemas are released as soon as possible. FossilOrigin-Name: 7a4ec57985fc5d980048bb7f1677452fb8cc4825cff8956760a1747b81b648bb	2020-01-18 18:59:15 +00:00
drh	0df48684bd	Fix the assert_schema_state_ok() routine so that it correctly ignores ATTACH-ed database that failed to open due to an error. FossilOrigin-Name: 1194a42add4119715347bb592feef352e4958d0c669c946d976a42049a712b68	2020-01-15 17:18:34 +00:00
drh	106ab91fc8	Merge all recent enhancements and fixes from trunk. FossilOrigin-Name: f783917800a5ce7c4bb31725b26d266cd4f133a0cc8414c6bf4789a8cd1e45c8	2020-01-15 14:26:58 +00:00
drh	806e04ab8f	Bring the reuse-schema branch up-to-date with version 3.30.0. FossilOrigin-Name: 6e09afecd6086211253b5f8eab718dde097f92a88100e54604a3f063c1a1fc98	2019-10-04 15:31:42 +00:00
drh	eb888e2497	Merge in the 3.30.0 beta 1 changes. FossilOrigin-Name: 067961241293b99b7f716e6f05e302b8354c9e7216296148b6f4ab59f8d3f4b0	2019-09-30 16:57:25 +00:00
drh	d973196e30	Merge all recent trunk enhancements into the reuse-schema branch. FossilOrigin-Name: 27eb223690989a294c5aad7a8ab1927904b1041e36ce7a0c04800bce49ec9142	2019-09-16 12:35:48 +00:00
dan	f6b6f46538	Merge latest trunk changes with this branch. FossilOrigin-Name: 5b4689d89cd27b238586ddee638b856145a9731ff70ffcb1659613528b792167	2019-08-13 15:22:10 +00:00
dan	f8f62070f8	In shared-schema mode, handle the case where a connection has created a virtual-table object, but is later assigned a different shared-schema object for which the virtual-table schema has not yet been initialized. FossilOrigin-Name: e30c7414fe483fcb68aeedd364dc5a3da62b01a80808a917016a9f148f1f3130	2019-08-09 14:54:44 +00:00
dan	73debcccd1	Fix spurious "no such table: x1" errors in shared-schema mode that could occur when a query that is a join across two or more databases needs to call the xConnect() methods of a virtual table. FossilOrigin-Name: edf45cd7c6c1122db961ae66c21c7e974115e6048f1f5014015a5f693f1844bf	2019-08-08 15:47:32 +00:00
dan	1430806e39	Fix a bug causing "no such table" and other similar sqlite3_prepare*() errors to return SQLITE_SCHEMA instead of SQLITE_ERROR in shared-schema mode when there is an attached database for which the schema has never been loaded. FossilOrigin-Name: 111e2c73cf430ae61e3f4cc34a1bee8ac7025b8a960fc3f3b7f493009b759ad7	2019-08-08 11:44:57 +00:00
dan	49c7657ac9	Add a multi-threaded test to threadtest3.c for the feature on this branch. FossilOrigin-Name: 62557fab0d21d47893e69d504ae2b4405c1837ccd6300a5a6743cb756eb28ad3	2019-08-06 15:02:49 +00:00
dan	e046ccb5f0	Add an assert() to the code on this branch. FossilOrigin-Name: fdd44bbb501c7252097e79685e916e760846e183bc9f022f9cf32f1d32f0089d	2019-08-06 11:45:33 +00:00
dan	0b5d397cb4	Merge latest changes from trunk into this branch. FossilOrigin-Name: 7f1e4e4b99644f986aa68bd40afddc4886145972eae1106347185eeff52150d6	2019-07-26 20:54:05 +00:00
drh	2833522a9a	Add a ctime.c entry for SQLITE_ENABLE_SHARED_SCHEMA. FossilOrigin-Name: 892ac94511a41dc4043ceb76aae267b1252d08fee41c475fb848c15519477adb	2019-07-18 19:50:54 +00:00
dan	06526fef2e	Modify the bits used for special flags on this branch to account for the fact that some of them are now used for other purposes. FossilOrigin-Name: 5a8d0f50f3c4dedfd7f97daba4cb1a8cfbe3bc44e0834199d4dd93a0d062ef81	2019-07-18 13:33:00 +00:00
drh	7e0410951f	Merge the version 3.29.0 release enhancements into the reuse-schema branch. FossilOrigin-Name: 9819ead089ef5ed92f529d9addbd89760ca5be7eacb3d209c99f639ec5761004	2019-07-10 18:45:50 +00:00
drh	abbad7ef3c	Merge recent trunk enhancements into the reuse-schema branch. FossilOrigin-Name: fae92fee54685cf0d44937e246e79652ee4679baa3bfb2774ff3ecf739a1e1e7	2019-07-08 21:32:00 +00:00
drh	cdfb4a29f4	Updates to the shared_schema.md notes document. FossilOrigin-Name: 51af2ade8eddae16a7290ab9676bcb4a677f0be72959640d0b664966398d8319	2019-06-03 14:02:58 +00:00
drh	ce86700aa7	In the CLI, add ".help" text for the .shared-schema command. FossilOrigin-Name: 3ba6f790e029f8c66b9ba16c657463606e6d45e095a498407154477c1358fbb2	2019-06-03 13:46:50 +00:00
drh	5593a4c26d	The ".shared-schema" command in the CLI requires the sqlite_dbpage table, so disable it if the build does not include that extension. FossilOrigin-Name: 0913ff4dc38290677357885ca40fe19ce45dafea6168a4e7403f0af083a48c65	2019-05-24 13:15:52 +00:00
drh	88e7099875	Merge recent enhancements from trunk. FossilOrigin-Name: ff9f3e09510b4418cb166fa2557598a279e7baedc315a5d1c3ae63beb92c238d	2019-05-24 13:04:55 +00:00
drh	28c156d6d6	Merge all the latest trunk enhancements into the reuse-schema branch. FossilOrigin-Name: 018f3199b9ba043fbbf88ec46b4fa16728f6507e000f4813ed346aaf6665add6	2019-05-14 22:25:26 +00:00
drh	e2e8e9b16f	Merge recent changes from trunk into reuse-schema FossilOrigin-Name: 5c6c9e7f6f83d565b317e3442e8bc664478adb407fe416d068fe0dcd17ffa5b5	2019-04-15 15:35:43 +00:00
dan	ff0e1d8d04	Remove a "puts" statement accidentally left in a test script. FossilOrigin-Name: 9f591ac07871958d173ae4cf9065c8000a9efb80676d158935d2700fff61a361	2019-03-26 19:14:50 +00:00
dan	98c5bff6c8	Add a few extra tests for SQLITE_STATUS_SCHEMA_USED with shared-schema databases. FossilOrigin-Name: e399fede7b27a70f90e363d987f23004d7015844f38d00d6d216433d70e4b901	2019-03-26 18:40:38 +00:00
drh	3eadd64c0e	Merge recent trunk enhancements. FossilOrigin-Name: db4e2cc36acca2708e9bd2e0febb4e1b3d6a6a3fa60d9bd6f2a49f4a8d1bc523	2019-03-26 11:57:50 +00:00
dan	d32261e7a9	Merge latest trunk changes with this branch. FossilOrigin-Name: 3196f5f480f221dc71bb92e6718a5c356782774be25df4df79dda0ac1101255a	2019-03-21 17:22:05 +00:00
dan	6847647dc4	Disable the feature on this branch in non-SQLITE_ENABLE_SHARED_SCHEMA builds. FossilOrigin-Name: b8e536089b0e6dec500a28556f826c99b78d979615ba3bc01ed31ead1b2112df	2019-03-21 17:13:55 +00:00
dan	ae070eff74	Use the IsReuseSchema() macro more consistently. Also, rename it to IsSharedSchema(). FossilOrigin-Name: c1be211c0286a6ff3ef8ab6839136175efb000118ff8704d3cc01b2a23b841ab	2019-03-20 20:02:03 +00:00
dan	f4c01da150	Fix an error message. FossilOrigin-Name: a70fdaa3903835dca338d68e750716fd3ab9dedbdfb2be6d6e058fd5fcb415fa	2019-03-20 19:17:45 +00:00
dan	0d46c528dd	Merge latest trunk changes into this branch. FossilOrigin-Name: 4cd20ca6776ef1c2f041fe6d30f84a3cf5f8a634eb34db2dce3217ee781d5848	2019-03-20 16:03:02 +00:00
dan	209f79234b	Merge latest trunk changes into this branch. FossilOrigin-Name: 97a9604d85cf5044e8109e533d4682b25bfe6a110f403ebd0fdef03880059f37	2019-03-04 07:25:38 +00:00
dan	22b16ac3d0	Update doc/shared_schema.md to describe the shell tool ".shared-schema" dot-command. FossilOrigin-Name: 0ce2092a5968d75d014fdc238391c362a9600c28bf18cdc631e98259a5278712	2019-02-26 16:36:21 +00:00
dan	88a96c49f2	Add new test file reuse5.test. For testing the shell tool ".shared-schema" command. FossilOrigin-Name: fa6008d547c6b24108a26e022f3f427fa19ffae006c88fee9de97d2244521de0	2019-02-26 16:13:43 +00:00
dan	85a76ddc12	Add the ".shared-schema check\|fix DB1 DB2..." command to the shell tool. For checking if a database is eligible to share an in-memory with the main database, and for fixing small problems that prevent it from being so. FossilOrigin-Name: 7d8e8a957235479fba568e1d3ff2cdfe4695184ee1a7ac64bce905a993725164	2019-02-26 15:43:45 +00:00
dan	20a434abd3	Fix a comment in build.c. FossilOrigin-Name: d6a9bff6f5cc52957deffe47fdba1197db111cac110760dec7680f91499a99f1	2019-02-25 19:23:01 +00:00
dan	9c2b284dbd	Merge latest trunk changes into this branch. FossilOrigin-Name: 5c1cf30859ed734eb2d6bc52adb057ca62a6b5a7eef66d8da1fa833e84468dee	2019-02-25 18:07:09 +00:00
dan	74e020a164	Where possible, avoid loading all schemas into memory for PRAGMA statements. FossilOrigin-Name: 64f97530ad387655767b5205fb9a9c723210cd4975176ab6fb71bca0cb585a74	2019-02-25 17:54:23 +00:00
dan	94dba01337	Merge latest trunk changes into this branch. FossilOrigin-Name: 001771afd0567c04736a778fc78fd7144492ae7c830e7f55de61869ce988f0ed	2019-02-22 17:44:58 +00:00
dan	239f69e204	Further test cases and fixes for SQLITE_OPEN_SHARED_SCHEMA. FossilOrigin-Name: ba0ab042f401a9d3b81dc546573214bbe2ad712c932aafcf0c045f189bbf09ca	2019-02-20 18:44:28 +00:00
dan	05a094d4c5	Add test and fixes for SQLITE_OPEN_SHARED_SCHEMA mode. FossilOrigin-Name: 9a78d89c8427ae737d4798cc146e41ada7cb83f4e39dcf3ac9469c510ed37673	2019-02-20 17:36:10 +00:00
dan	aec53fa5ba	Improve error messages caused by corrupt database schemas in OPEN_SHARED_SCHEMA mode. FossilOrigin-Name: 8ac75b8a880447ea67cf7646fc5af1379ce35861f396634119d7381e1dde404a	2019-02-19 18:00:28 +00:00
dan	a011145aae	Ensure that creating temp schema items does not cause an OPEN_SHARABLE_SCHEMA connection to load all schemas into memory. FossilOrigin-Name: 88cbf54eee7845f9e40e6879fc38eb98a80e81c987b7edeb39f3058590003347	2019-02-18 18:16:05 +00:00
dan	13af9ba7af	Enhance the virtual table in test_schemapool.c so that it can be used to check that SHARED_SCHEMA connections are not allocating and freeing schemas when they should not be. FossilOrigin-Name: cb236cb98564b870317ba3e481a3c7d7f9769b0294a01246bcb724f04e1e7b10	2019-02-15 19:36:47 +00:00
dan	6170a98cfa	Fix a problem with eponymous virtual tables and SHARED_SCHEMA databases. Also, after preparing statements that require all database schemas (REINDEX, ANALYZE, CREATE, DROP and some PRAGMA statements), do not allow the database connection to return more than one schema to each schema-pool. FossilOrigin-Name: ecf6251ec0bb745a4ef9bad9f9ecd3babb687a3806fd96554b265313625270c5	2019-02-15 19:00:41 +00:00
dan	d0932d5358	Revert the rearrangement of VDBE code in [219b39e14] so that vdbe.c matches trunk. Since the new call to sqlite3Init() in OP_ParseSchema was removed, the rearrangement no longer provides any performance advantage. FossilOrigin-Name: 03c4f00317233a34f29e1218786166d17837d47206532a29d2713093f01adea5	2019-02-15 11:54:57 +00:00
dan	61155cb70b	Fix SQLITE_DBSTATUS_SCHEMA_USED so that it works with SQLITE_OPEN_SHARED_SCHEMA connections. FossilOrigin-Name: d43b3c056cb13930865c504c9498b2c83e4bebce9bff01ee21293e7dc7a6711e	2019-02-14 21:04:27 +00:00
dan	d746d250f0	Change the name of the SQLITE_OPEN_REUSE_SCHEMA flag to SQLITE_OPEN_SHARED_SCHEMA. FossilOrigin-Name: 7257fcc8c990b46a4f6a9e506f4a4a40195e6b2c626efd380cfa01f0ce8eb0fb	2019-02-14 18:38:44 +00:00
dan	155a112b81	Fix a typo in shared_schema.md. FossilOrigin-Name: e47a5aea76560e86e5417fea9e2219ec6c30e47ef383e499cfe927f64d584dac	2019-02-14 17:59:36 +00:00
dan	a5150d4f05	Add documentation file doc/shared_schema.md to describe the change on this branch. FossilOrigin-Name: a5f8067dde1e8974f779ab838a02416a7dd9d20d253af860d08d635cfede6fee	2019-02-14 17:51:38 +00:00
dan	64104062a7	Merge latest trunk into this branch. FossilOrigin-Name: 577d1638362666a8220401d0d0d8bfb3c028ab09e7def1e4bf195db37269c22f	2019-02-14 15:56:59 +00:00
dan	1395c92f1f	Add missing comments and fix other code issues in the new functions in callback.c. FossilOrigin-Name: 441cabb62fe14bbef8b19066941426eeb2de128564ec2bfb762228fdae794447	2019-02-14 15:47:18 +00:00
dan	33a37f5ef0	Fix for sqlite3_table_column_metadata() on REUSE_SCHEMA databases. FossilOrigin-Name: 53220ad7809954eb4118d9127849efa82787f43898af00c9127cd4998a12c619	2019-02-13 19:17:30 +00:00
dan	9d65677e57	Avoid crashing after parsing a corrupt schema with a REUSE_SCHEMA connection. FossilOrigin-Name: b102148e71c0102eedbf28d9bc8ea8d9bd742eac45ee7f1b08ece60bcdab5036	2019-02-13 18:29:49 +00:00
dan	6758315c8e	Fix a problem with the incrblob API and reusable schemas. FossilOrigin-Name: 34f0f96f47040df1e305ac9fd4664c5ed4246580e22a00573c73d6528a5725b5	2019-02-13 15:51:07 +00:00
drh	5944230305	Rearrange the code in the VDBE to help out the C-compiler optimizer. And fix a harmless compiler warning. FossilOrigin-Name: 219b39e149a0334b577e094e066e1ca2fe686b408468e9f196611490f3a82810	2019-02-13 14:06:56 +00:00
drh	a72a438cd7	Performance optimization in the VDBE, and a fix for a harmless compiler warning. FossilOrigin-Name: e002666ac79c3452a772323c6ecc696104341cd842e77541553ec028f188096b	2019-02-13 13:48:48 +00:00
dan	d62150108a	Fix a problem with OPEN_REUSE_SCHEMA connections reloading the temp schema. FossilOrigin-Name: 7c2ec2d4cfcda9c0aa6d57bd9a12ff98b78e648533d49da27f91d5a37bf1e001	2019-02-13 08:40:34 +00:00
dan	2ce6757bd4	Add tests for creating temp schema objects with SQLITE_OPEN_REUSE_SCHEMA connections. FossilOrigin-Name: 8c07b609fccc43795498b942c733896defd8887e4ddd9e0ef48c124dfcf9fd7f	2019-02-12 20:58:34 +00:00
dan	33d1394e1a	Share schemas between databases attached to the same database handle. FossilOrigin-Name: ea611d7cba604dc901c8088ccfa13367a5ee75f9499ea8d8b62a590daac2eae0	2019-02-12 19:20:33 +00:00
dan	81fb4ef019	Merge latest trunk changes into this branch. FossilOrigin-Name: dbedd81bf2e29ae9ed88526c1cc97e5c4d0a256ad7d960304bbb5e15c44f51f0	2019-02-11 20:13:13 +00:00
dan	d4e11dd78f	Add eponymous virtual table "schemapool". For inspecting the current contents of the schema-pool. FossilOrigin-Name: 2ebeb747832bd53284ab23b4c2558f0fa550c0ea2b4a6c1640eeb83f8132c556	2019-02-11 19:34:38 +00:00
dan	5add6f25e2	Fix virtual table support for SQLITE_OPEN_REUSABLE_SCHEMA connections. FossilOrigin-Name: 3ca8856a7b1c36885cea007b8fb05b59f1fdc9d4b54436819193f498519a23c7	2019-02-09 17:47:14 +00:00
dan	30fdc47579	Add test cases and fix problems on this branch. FossilOrigin-Name: 2b2e9f81cdc7a3ac1eacc087fbd0414ead732878aae296bab6b54b4a7cd0a06e	2019-02-08 19:30:09 +00:00
dan	73e6f3adbd	Merge latest trunk into this branch. FossilOrigin-Name: c089cc4fbe2e5e53d76154146870d14fc3b8d342a49580e41a5616817099715c	2019-02-05 19:51:15 +00:00
dan	73b8e1f2d6	Fix memory leaks on this branch. FossilOrigin-Name: e9c5e1891ff4f7e57131031f068efea87027ddab0cd7846e0514a105853be47d	2019-02-05 19:15:36 +00:00
dan	01d6eab9a5	Fix a problem with reloading the schema on this branch. FossilOrigin-Name: 5dfbef8349e47f9d9fcdbb648ecd18b5bc7eebdb1a3ddaf91789d036b7de8a90	2019-02-04 21:02:00 +00:00
dan	e54087db7b	Try new approach ensuring that each Schema object is only used by one connection/database at any one time. FossilOrigin-Name: 9e8e5f52cf90579c3071f04a3c6857bb76b4ca1b1900a7f865de789ed0bb8678	2019-02-02 21:02:22 +00:00
dan	d000f2286d	Merge latest trunk changes with this branch. FossilOrigin-Name: ae88f8e1ffc33748e45308c21ba83499228ae05344df81e41dd61e14a1270588	2018-11-09 18:44:45 +00:00
drh	8874678ecd	Add the ability to open a database connection in -reuseschema mode in the CLI. Adjust memory allocation accounting so that a shared schema is allocated across each database sharing it. FossilOrigin-Name: 3869b2106b9a639b5e739dc9f9acd2f7a9223d3ce562297b877c5d4d2bf76468	2018-10-08 23:29:05 +00:00
dan	8612853f70	Fix a problem with using virtual tables via reuse-schema connections. FossilOrigin-Name: e5897dafda2b003c34eeecb44e091e2ac0d8589c9db728a0b02fb56966cfc9b7	2018-10-08 20:57:35 +00:00
drh	62012c0b34	Merge fixes from trunk. FossilOrigin-Name: 9c8255a199d6544b02302bfe3ecd253098821170646a509d2e3dc6cf4e43289b	2018-10-08 20:37:21 +00:00
dan	7d3159668c	Merge latest trunk changes into this branch. FossilOrigin-Name: 2ac72114a1f5344b42472b941c60f460c28c981a22ea40909b30f7bf4eb4b11b	2018-10-08 18:58:51 +00:00
dan	d6af93a92c	Add experimental sqlite3_open_v2() flag SQLITE_OPEN_REUSE_SCHEMA. For sharing identical in-memory schema objects between connections. FossilOrigin-Name: a625698048c05375f12ea8875892fdbf3518291f10917fe68dd2294280cd3b42	2017-08-09 20:35:10 +00:00
@@ -1 +1 @@
 .35.0
 .34.1