Change the code generator for UPDATE to generate code in an order that might

run more efficiently in many cases.

FossilOrigin-Name: c6239bf943fc42b8fc1ece95c9268240b7c53e80

Makefile.msc

@@ -292,9 +292,9 @@ NSDKLIBPATH = $(NSDKLIBPATH:\\=\)
 # will run on the platform that is doing the build.
 #
 !IF $(USE_FULLWARN)!=0
-BCC = $(NCC) -nologo -W4
+BCC = $(NCC) -nologo -W4 $(CCOPTS) $(BCCOPTS)
 !ELSE
-BCC = $(NCC) -nologo -W3
+BCC = $(NCC) -nologo -W3 $(CCOPTS) $(BCCOPTS)
 !ENDIF
 
 # Check if assembly code listings should be generated for the source
@@ -322,13 +322,13 @@ NLTLIBPATHS = $(NLTLIBPATHS) "/LIBPATH:$(NUCRTLIBPATH)"
 # same unless your are cross-compiling.)
 #
 !IF $(USE_FULLWARN)!=0
-TCC = $(CC) -nologo -W4 -DINCLUDE_MSVC_H=1
+TCC = $(CC) -nologo -W4 -DINCLUDE_MSVC_H=1 $(CCOPTS) $(TCCOPTS)
 !ELSE
-TCC = $(CC) -nologo -W3
+TCC = $(CC) -nologo -W3 $(CCOPTS) $(TCCOPTS)
 !ENDIF
 
 TCC = $(TCC) -DSQLITE_OS_WIN=1 -I. -I$(TOP) -I$(TOP)\src -fp:precise
-RCC = $(RC) -DSQLITE_OS_WIN=1 -I$(TOP) -I$(TOP)\src
+RCC = $(RC) -DSQLITE_OS_WIN=1 -I$(TOP) -I$(TOP)\src $(RCOPTS) $(RCCOPTS)
 
 # Check if we want to use the "stdcall" calling convention when compiling.
 # This is not supported by the compilers for non-x86 platforms.  It should
@@ -800,7 +800,9 @@ LTLINKOPTS = $(LTLINKOPTS) "/LIBPATH:$(PSDKLIBPATH)"
 # If either debugging or symbols are enabled, enable PDBs.
 #
 !IF $(DEBUG)>1 || $(SYMBOLS)!=0
-LDFLAGS = /DEBUG
+LDFLAGS = /DEBUG $(LDOPTS)
+!ELSE
+LDFLAGS = $(LDOPTS)
 !ENDIF
 
 # Start with the Tcl related linker options.

VERSION

@@ -1 +1 @@
-3.9.0
+3.9.1

configure

@@ -1,6 +1,6 @@
 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.69 for sqlite 3.9.0.
+# Generated by GNU Autoconf 2.69 for sqlite 3.9.1.
 #
 #
 # Copyright (C) 1992-1996, 1998-2012 Free Software Foundation, Inc.
@@ -726,8 +726,8 @@ MAKEFLAGS=
 # Identity of this package.
 PACKAGE_NAME='sqlite'
 PACKAGE_TARNAME='sqlite'
-PACKAGE_VERSION='3.9.0'
-PACKAGE_STRING='sqlite 3.9.0'
+PACKAGE_VERSION='3.9.1'
+PACKAGE_STRING='sqlite 3.9.1'
 PACKAGE_BUGREPORT=''
 PACKAGE_URL=''
 
@@ -1458,7 +1458,7 @@ if test "$ac_init_help" = "long"; then
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures sqlite 3.9.0 to adapt to many kinds of systems.
+\`configure' configures sqlite 3.9.1 to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1523,7 +1523,7 @@ fi
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of sqlite 3.9.0:";;
+     short | recursive ) echo "Configuration of sqlite 3.9.1:";;
    esac
   cat <<\_ACEOF
 
@@ -1643,7 +1643,7 @@ fi
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-sqlite configure 3.9.0
+sqlite configure 3.9.1
 generated by GNU Autoconf 2.69
 
 Copyright (C) 2012 Free Software Foundation, Inc.
@@ -2062,7 +2062,7 @@ cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by sqlite $as_me 3.9.0, which was
+It was created by sqlite $as_me 3.9.1, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   $ $0 $@
@@ -11946,7 +11946,7 @@ cat >>$CONFIG_STATUS <<\_ACEOF || ac_write_fail=1
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by sqlite $as_me 3.9.0, which was
+This file was extended by sqlite $as_me 3.9.1, which was
 generated by GNU Autoconf 2.69.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -12012,7 +12012,7 @@ _ACEOF
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 ac_cs_config="`$as_echo "$ac_configure_args" | sed 's/^ //; s/[\\""\`\$]/\\\\&/g'`"
 ac_cs_version="\\
-sqlite config.status 3.9.0
+sqlite config.status 3.9.1
 configured by $0, generated by GNU Autoconf 2.69,
   with options \\"\$ac_cs_config\\"
 

ext/misc/json1.c

@@ -28,7 +28,6 @@
 SQLITE_EXTENSION_INIT1
 #include <assert.h>
 #include <string.h>
-#include <ctype.h>  /* amalgamator: keep */
 #include <stdlib.h>
 #include <stdarg.h>
 
@@ -43,8 +42,17 @@ SQLITE_EXTENSION_INIT1
 ** Versions of isspace(), isalnum() and isdigit() to which it is safe
 ** to pass signed char values.
 */
-#define safe_isdigit(x) isdigit((unsigned char)(x))
-#define safe_isalnum(x) isalnum((unsigned char)(x))
+#ifdef sqlite3Isdigit
+   /* Use the SQLite core versions if this routine is part of the
+   ** SQLite amalgamation */
+#  define safe_isdigit(x) sqlite3Isdigit(x)
+#  define safe_isalnum(x) sqlite3Isalnum(x)
+#else
+   /* Use the standard library for separate compilation */
+#include <ctype.h>  /* amalgamator: keep */
+#  define safe_isdigit(x) isdigit((unsigned char)(x))
+#  define safe_isalnum(x) isalnum((unsigned char)(x))
+#endif
 
 /*
 ** Growing our own isspace() routine this way is twice as fast as
@@ -52,7 +60,7 @@ SQLITE_EXTENSION_INIT1
 ** increase for the parser.  (Ubuntu14.10 gcc 4.8.4 x64 with -Os).
 */
 static const char jsonIsSpace[] = {
-  0, 0, 0, 0, 0, 0, 0, 0,     0, 1, 1, 0, 1, 1, 0, 0,
+  0, 0, 0, 0, 0, 0, 0, 0,     0, 1, 1, 0, 0, 1, 0, 0,
   0, 0, 0, 0, 0, 0, 0, 0,     0, 0, 0, 0, 0, 0, 0, 0,
   1, 0, 0, 0, 0, 0, 0, 0,     0, 0, 0, 0, 0, 0, 0, 0,
   0, 0, 0, 0, 0, 0, 0, 0,     0, 0, 0, 0, 0, 0, 0, 0,
@@ -514,7 +522,13 @@ static void jsonReturn(
       int_as_real: /* fall through to real */;
     }
     case JSON_REAL: {
-      double r = strtod(pNode->u.zJContent, 0);
+      double r;
+#ifdef SQLITE_AMALGAMATION
+      const char *z = pNode->u.zJContent;
+      sqlite3AtoF(z, &r, sqlite3Strlen30(z), SQLITE_UTF8);
+#else
+      r = strtod(pNode->u.zJContent, 0);
+#endif
       sqlite3_result_double(pCtx, r);
       break;
     }

manifest

@@ -1,10 +1,10 @@
-C Merge\supdates\sfrom\strunk.
-D 2015-10-15T21:12:27.435
+C Change\sthe\scode\sgenerator\sfor\sUPDATE\sto\sgenerate\scode\sin\san\sorder\sthat\smight\nrun\smore\sefficiently\sin\smany\scases.
+D 2015-10-17T01:00:03.352
 F Makefile.in 2ea961bc09e441874eb3d1bf7398e04feb24f3ee
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
-F Makefile.msc 8e42cb55739cd8c12e1fd25401956e2019448f6a
+F Makefile.msc 4eb750e0fdf52050a06d881e1b060f4bb116ed7e
 F README.md 8ecc12493ff9f820cdea6520a9016001cb2e59b7
-F VERSION cacf16a72f9a03cd06b939a764e32f6f53254c7f
+F VERSION a47917b59f38b632b3a8662d14fd20f94956bdd0
 F aclocal.m4 a5c22d164aff7ed549d53a90fa56d56955281f50
 F art/sqlite370.eps aa97a671332b432a54e1d74ff5e8775be34200c2
 F art/sqlite370.ico af56c1d00fee7cd4753e8631ed60703ed0fc6e90
@@ -35,7 +35,7 @@ F autoconf/tea/win/rules.vc c511f222b80064096b705dbeb97060ee1d6b6d63
 F config.guess 226d9a188c6196f3033ffc651cbc9dcee1a42977
 F config.h.in 42b71ad3fe21c9e88fa59e8458ca1a6bc72eb0c0
 F config.sub 9ebe4c3b3dab6431ece34f16828b594fb420da55
-F configure 99485c9c0446d1236a78a53de6f2737f45f0aca5 x
+F configure 762a66c6eb9331f8af21f5d00b610bd61eaf8e14 x
 F configure.ac f36bd4fb8c53eed8374c5a5ef319807c08c23fa9
 F contrib/sqlitecon.tcl 210a913ad63f9f991070821e599d600bd913e0ad
 F doc/lemon.html 334dbf6621b8fb8790297ec1abf3cfa4621709d1
@@ -195,7 +195,7 @@ F ext/misc/eval.c f971962e92ebb8b0a4e6b62949463ee454d88fa2
 F ext/misc/fileio.c d4171c815d6543a9edef8308aab2951413cd8d0f
 F ext/misc/fuzzer.c 4c84635c71c26cfa7c2e5848cf49fe2d2cfcd767
 F ext/misc/ieee754.c b0362167289170627659e84173f5d2e8fee8566e
-F ext/misc/json1.c fed5b948168f26f39e67d898b03d93dd00e75196
+F ext/misc/json1.c 4f45afd9dbcd6feca8c528251efbb7fc09299a09
 F ext/misc/nextchar.c 35c8b8baacb96d92abbb34a83a997b797075b342
 F ext/misc/percentile.c bcbee3c061b884eccb80e21651daaae8e1e43c63
 F ext/misc/regexp.c af92cdaa5058fcec1451e49becc7ba44dba023dc
@@ -280,7 +280,7 @@ F src/auth.c b56c78ebe40a2110fd361379f7e8162d23f92240
 F src/backup.c c3a9c4209439b806c44cf30daf466955727bf46c
 F src/bitvec.c d1f21d7d91690747881f03940584f4cc548c9d3d
 F src/btmutex.c 45a968cc85afed9b5e6cf55bf1f42f8d18107f79
-F src/btree.c 0b74bc28b2dc907cba03b5b4b3b81584273be699
+F src/btree.c ea8c62f65e57e49bd6b0988cd681aca7246b51af
 F src/btree.h 40189aefdc2b830d25c8b58fd7d56538481bfdd7
 F src/btreeInt.h 8177c9ab90d772d6d2c6c517e05bed774b7c92c0
 F src/build.c d6162335d690396dfc5c4bd59e8b2b0c14ba6285
@@ -290,7 +290,7 @@ F src/ctime.c 509ef9c64d1321f42448f111da86400b1799218a
 F src/date.c fb1c99172017dcc8e237339132c91a21a0788584
 F src/dbstat.c e637e7a7ff40ef32132a418c6fdf1cfb63aa27c7
 F src/delete.c 35c939eb8bacc9dd8a6715964e5f69feb8c20e44
-F src/expr.c e8765542b21bc7ff801ca82d5cf11f0b13a219af
+F src/expr.c d9896fda47a8f67d0ed203e1fa981444424200c6
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c 31900763094a3736a5fc887469202eb579fef2d0
 F src/func.c ecdd69ec6a1e406f04cc73324be2ebbf6354197f
@@ -303,7 +303,7 @@ F src/journal.c b4124532212b6952f42eb2c12fa3c25701d8ba8d
 F src/legacy.c ba1863ea58c4c840335a84ec276fc2b25e22bc4e
 F src/lempar.c d344a95d60c24e2f490ee59db9784b1b17439012
 F src/loadext.c 18586e45a215325f15096821e9c082035d4fb810
-F src/main.c 2082c1c7aa1687849848581e084f6046c503841d
+F src/main.c fec97668771438033a7559883401067b139729e1
 F src/malloc.c 0a2e42b835c980ba91c17866e9b6a9810ff54d75
 F src/mem0.c 6a55ebe57c46ca1a7d98da93aaa07f99f1059645
 F src/mem1.c 52485a88f22649c3b3b4f3eb15760505d49ccf71
@@ -312,11 +312,11 @@ F src/mem3.c 8768ac94694f31ffaf8b4d0ea5dc08af7010a35a
 F src/mem5.c c1ab1153bd6443bdf6f71e4213c6fb31221b9eb7
 F src/memjournal.c 3eb2c0b51adbd869cb6a44780323f05fa904dc85
 F src/msvc.h d9ba56c6851227ab44b3f228a35f3f5772296495
-F src/mutex.c 40dc52f7525fa86f35dff2a7c9b6e6870240952a
+F src/mutex.c 8e45800ee78e0cd1f1f3fe8e398853307f4a085c
 F src/mutex.h 779d588e3b7756ec3ecf7d78cde1d84aba414f85
-F src/mutex_noop.c f03e26ba8258399da23b51234f6b6a97197c1900
-F src/mutex_unix.c 77d84839735aec71f9fe731bfd845d81cec2bb65
-F src/mutex_w32.c c3a5049bc413dd8321480b28f275fbf2b99c846e
+F src/mutex_noop.c 9d4309c075ba9cc7249e19412d3d62f7f94839c4
+F src/mutex_unix.c a94b46f3f7beba307dde1b298b0f99f9c3677a93
+F src/mutex_w32.c 5e6fe1c298fb5a8a15aaed4161d5759311431c17
 F src/notify.c 9711a7575036f0d3040ba61bc6e217f13a9888e7
 F src/os.c 8fd25588eeba74068d41102d26810e216999b6c8
 F src/os.h 3e57a24e2794a94d3cf2342c6d9a884888cd96bf
@@ -343,7 +343,7 @@ F src/shell.c d25df04168d6ba5a4fa05bdbf859df667f9eb621
 F src/sqlite.h.in 839c818e16ea68703d90d17bd2bb3607191debce
 F src/sqlite3.rc 992c9f5fb8285ae285d6be28240a7e8d3a7f2bad
 F src/sqlite3ext.h 4b66e3e3435da4b4c8c83696d0349f0c503b3924
-F src/sqliteInt.h 2d82464793c7d07b01dfcdc43942a27063ea398d
+F src/sqliteInt.h 1ad779ee62efee60494af0a75d8d45592f9f53c3
 F src/sqliteLimit.h 216557999cb45f2e3578ed53ebefe228d779cb46
 F src/status.c 286f6398a4d2cd1e8ff0771e3d30f8dddb4768ea
 F src/table.c 51b46b2a62d1b3a959633d593b89bab5e2c9155e
@@ -397,17 +397,17 @@ F src/threads.c bbfb74450643cb5372a43ad4f6cffd7e9dfcecb0
 F src/tokenize.c 338bc8f7c9dd103188952cda7964696bacac6d22
 F src/treeview.c 154f0acc622fa3514de8777dcedf4c8a8802b4ce
 F src/trigger.c 322f23aad694e8f31d384dcfa386d52a48d3c52f
-F src/update.c aa10336a2719bd1b9f89004f3d7ba6d566623a49
+F src/update.c 04ed5f0334d313221cd084d46c5c2e0ad29ecb52
 F src/utf.c fc6b889ba0779b7722634cdeaa25f1930d93820c
 F src/util.c fc612367108b74573c5fd13a85d0a23027f438bd
 F src/vacuum.c 2ddd5cad2a7b9cef7f9e431b8c7771634c6b1701
-F src/vdbe.c 61bd96c72f103d2e96de6ab7852dc009dc9bb6b3
+F src/vdbe.c e9315575bed64f9aa559151283c873be34143914
 F src/vdbe.h 4bc88bd0e06f8046ee6ab7487c0015e85ad949ad
-F src/vdbeInt.h 8b867eac234e28627ffcace3cd4b4b79bbec664b
+F src/vdbeInt.h 777dd76d513347acb1a71d94df2be00516add637
 F src/vdbeapi.c 020681b943e77766b32ae1cddf86d7831b7374ca
-F src/vdbeaux.c fd00b489ab3f44f2dca1e4344faf289b7bfcf649
+F src/vdbeaux.c 906bc74ea90707b57a23e4264727fff7b48d0cb5
 F src/vdbeblob.c 565fabd302f5fca3bdf3d56cac330483616a39b6
-F src/vdbemem.c 19b3036aa4d676e7103b0fb5efd6327da455f915
+F src/vdbemem.c fdd1578e47bea61390d472de53c565781d81e045
 F src/vdbesort.c 8b23930a1289526f6d2a3a9f2e965bcc963e4a68
 F src/vdbetrace.c 8befe829faff6d9e6f6e4dee5a7d3f85cc85f1a0
 F src/vtab.c 2a8b44aa372c33f6154208e7a7f6c44254549806
@@ -815,7 +815,7 @@ F test/journal3.test ff8af941f9e06161d3db1b46bb9f965ff0e7f307
 F test/jrnlmode.test 7864d59cf7f6e552b9b99ba0f38acd167edc10fa
 F test/jrnlmode2.test 81610545a4e6ed239ea8fa661891893385e23a1d
 F test/jrnlmode3.test 556b447a05be0e0963f4311e95ab1632b11c9eaa
-F test/json101.test 83e6ebfb3cef6329853ab854403ec82b1787b537
+F test/json101.test f0178422b3a2418f423fd0d3caf3571c8d1b9863
 F test/json102.test bf3fe7a706d30936a76a0f7a0375e1e8e73aff5a
 F test/keyword1.test 37ef6bba5d2ed5b07ecdd6810571de2956599dff
 F test/lastinsert.test 42e948fd6442f07d60acbd15d33fb86473e0ef63
@@ -1341,7 +1341,7 @@ F tool/checkSpacing.c 810e51703529a204fc4e1eb060e9ab663e3c06d2
 F tool/extract.c 054069d81b095fbdc189a6f5d4466e40380505e2
 F tool/fast_vacuum.c 5ba0d6f5963a0a63bdc42840f678bad75b2ebce1
 F tool/fragck.tcl 5265a95126abcf6ab357f7efa544787e5963f439
-F tool/fuzzershell.c 87cc3d6f00239d786d231954289f106131989cc7
+F tool/fuzzershell.c b36096cdbcb4af985a2d6c20093d61e55b49bfe1
 F tool/genfkey.README cf68fddd4643bbe3ff8e31b8b6d8b0a1b85e20f4
 F tool/genfkey.test 4196a8928b78f51d54ef58e99e99401ab2f0a7e5
 F tool/getlock.c f4c39b651370156cae979501a7b156bdba50e7ce
@@ -1387,11 +1387,14 @@ F tool/symbols.sh fec58532668296d7c7dc48be9c87f75ccdb5814f
 F tool/tostr.tcl 96022f35ada2194f6f8ccf6fd95809e90ed277c4
 F tool/varint.c 5d94cb5003db9dbbcbcc5df08d66f16071aee003
 F tool/vdbe-compress.tcl 5926c71f9c12d2ab73ef35c29376e756eb68361c
-F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
+F tool/vdbe_profile.tcl 246d0da094856d72d2c12efec03250d71639d19f
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 48bd54594752d5be3337f12c72f28d2080cb630b
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 8d69983dc2b94ca752259dcec360c32d60a8e9dd 871e091df651b2275a672c35ff938bd4b6db0d7f
-R 2967669474e0bc8a932a9ea55508690e
-U mistachkin
-Z 30c10e55f7847c468e81b5b9567db928
+P 0df371d1a51c2028aefa4c704707773750317689
+R 54a047417394c2361e73646ac2a70fb9
+T *branch * improved-update
+T *sym-improved-update *
+T -sym-trunk *
+U drh
+Z 6145fe123cad180747a41342b799e5b4

manifest.uuid

@@ -1 +1 @@
-a447cf90ddfd2930274f58de4bae3b07f2886632
+c6239bf943fc42b8fc1ece95c9268240b7c53e80

src/btree.c

@@ -4499,7 +4499,9 @@ static int accessPayload(
 
       /* If required, populate the overflow page-list cache. */
       if( (pCur->curFlags & BTCF_ValidOvfl)!=0 ){
-        assert(!pCur->aOverflow[iIdx] || pCur->aOverflow[iIdx]==nextPage);
+        assert( pCur->aOverflow[iIdx]==0
+                || pCur->aOverflow[iIdx]==nextPage
+                || CORRUPT_DB );
         pCur->aOverflow[iIdx] = nextPage;
       }
 

src/expr.c

@@ -3356,6 +3356,10 @@ void sqlite3ExprCodeAndCache(Parse *pParse, Expr *pExpr, int target){
 **
 ** The SQLITE_ECEL_FACTOR argument allows constant arguments to be
 ** factored out into initialization code.
+**
+** The SQLITE_ECEL_REF flag means that expressions in the list with
+** ExprList.a[].u.x.iOrderByCol>0 have already been evaluated and stored
+** in registers at srcReg, and so the value can be copied from there.
 */
 int sqlite3ExprCodeExprList(
   Parse *pParse,     /* Parsing context */

src/main.c

@@ -391,18 +391,14 @@ int sqlite3_config(int op, ...){
 #if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0 /* IMP: R-63666-48755 */
     case SQLITE_CONFIG_MUTEX: {
       /* Specify an alternative mutex implementation */
-      sqlite3MutexCopy(&sqlite3GlobalConfig.mutex,
-                       va_arg(ap, sqlite3_mutex_methods*));
-      sqlite3MemoryBarrier();
+      sqlite3GlobalConfig.mutex = *va_arg(ap, sqlite3_mutex_methods*);
       break;
     }
 #endif
 #if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0 /* IMP: R-14450-37597 */
     case SQLITE_CONFIG_GETMUTEX: {
       /* Retrieve the current mutex implementation */
-      sqlite3MemoryBarrier();
-      sqlite3MutexCopy(va_arg(ap, sqlite3_mutex_methods*),
-                       &sqlite3GlobalConfig.mutex);
+      *va_arg(ap, sqlite3_mutex_methods*) = sqlite3GlobalConfig.mutex;
       break;
     }
 #endif

src/mutex.c

@@ -26,49 +26,35 @@ static SQLITE_WSD int mutexIsInit = 0;
 
 
 #ifndef SQLITE_MUTEX_OMIT
-/*
-** Copies a mutex implementation.  Both arguments must point to valid
-** memory.
-*/
-void sqlite3MutexCopy(
-  sqlite3_mutex_methods *pTo,
-  sqlite3_mutex_methods const *pFrom
-){
-  pTo->xMutexInit = pFrom->xMutexInit;
-  pTo->xMutexEnd = pFrom->xMutexEnd;
-  pTo->xMutexFree = pFrom->xMutexFree;
-  pTo->xMutexEnter = pFrom->xMutexEnter;
-  pTo->xMutexTry = pFrom->xMutexTry;
-  pTo->xMutexLeave = pFrom->xMutexLeave;
-  pTo->xMutexHeld = pFrom->xMutexHeld;
-  pTo->xMutexNotheld = pFrom->xMutexNotheld;
-  pTo->xMutexAlloc = pFrom->xMutexAlloc;
-}
-
 /*
 ** Initialize the mutex system.
 */
 int sqlite3MutexInit(void){ 
-  int rc;
-
-  sqlite3MemoryBarrier();
-  if( sqlite3CompareAndSwap(
-                   (void * volatile *)&sqlite3GlobalConfig.mutex.xMutexAlloc,
-                   0, sqlite3GlobalConfig.mutex.xMutexAlloc)==0 ){
+  int rc = SQLITE_OK;
+  if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
     /* If the xMutexAlloc method has not been set, then the user did not
     ** install a mutex implementation via sqlite3_config() prior to 
     ** sqlite3_initialize() being called. This block copies pointers to
     ** the default implementation into the sqlite3GlobalConfig structure.
     */
     sqlite3_mutex_methods const *pFrom;
+    sqlite3_mutex_methods *pTo = &sqlite3GlobalConfig.mutex;
 
     if( sqlite3GlobalConfig.bCoreMutex ){
       pFrom = sqlite3DefaultMutex();
     }else{
       pFrom = sqlite3NoopMutex();
     }
-    sqlite3MutexCopy(&sqlite3GlobalConfig.mutex, pFrom);
+    pTo->xMutexInit = pFrom->xMutexInit;
+    pTo->xMutexEnd = pFrom->xMutexEnd;
+    pTo->xMutexFree = pFrom->xMutexFree;
+    pTo->xMutexEnter = pFrom->xMutexEnter;
+    pTo->xMutexTry = pFrom->xMutexTry;
+    pTo->xMutexLeave = pFrom->xMutexLeave;
+    pTo->xMutexHeld = pFrom->xMutexHeld;
+    pTo->xMutexNotheld = pFrom->xMutexNotheld;
     sqlite3MemoryBarrier();
+    pTo->xMutexAlloc = pFrom->xMutexAlloc;
   }
   assert( sqlite3GlobalConfig.mutex.xMutexInit );
   rc = sqlite3GlobalConfig.mutex.xMutexInit();

src/mutex_noop.c

@@ -29,28 +29,6 @@
 
 #ifndef SQLITE_MUTEX_OMIT
 
-/*
-** Try to provide an atomic compare-and-swap operation on a void pointer,
-** needed for initialization only.
-*/
-void *sqlite3NoopCompareAndSwap(
-  void *volatile *pCurVal,
-  void *cmpVal,
-  void *swapVal
-){
-  /*
-  ** This platform may not have a way to perform an atomic compare-and-swap
-  ** operation; therefore, use the fallback algorithm.
-  **
-  ** WARNING: This code is almost certainly not thread-safe.
-  */
-  void *oldVal = *pCurVal;
-  if( oldVal==cmpVal ){
-    *pCurVal = swapVal;
-  }
-  return oldVal;
-}
-
 #ifndef SQLITE_DEBUG
 /*
 ** Stub routines for all mutex methods.

src/mutex_unix.c

@@ -93,34 +93,6 @@ void sqlite3MemoryBarrier(void){
 #endif
 }
 
-/*
-** Try to provide an atomic compare-and-swap operation on a void pointer,
-** needed for initialization only.
-*/
-void *sqlite3CompareAndSwap(
-  void *volatile *pCurVal,
-  void *cmpVal,
-  void *swapVal
-){
-#if defined(SQLITE_COMPARE_AND_SWAP)
-  return SQLITE_COMPARE_AND_SWAP(pCurVal, cmpVal, swapVal);
-#elif defined(__GNUC__) && GCC_VERSION>=4001000 && SQLITE_PTRSIZE>4
-  return (void *)__sync_val_compare_and_swap_8(
-      (u64 volatile *)pCurVal, (u64)cmpVal, (u64)swapVal);
-#elif defined(__GNUC__) && GCC_VERSION>=4001000
-  return (void *)__sync_val_compare_and_swap_4(
-      (u32 volatile *)pCurVal, (u32)cmpVal, (u32)swapVal);
-#else
-  /*
-  ** This platform may not have a way to perform an atomic compare-and-swap
-  ** operation; therefore, use the fallback algorithm.
-  **
-  ** WARNING: This code is almost certainly not thread-safe.
-  */
-  return sqlite3NoopCompareAndSwap(pCurVal, cmpVal, swapVal);
-#endif
-}
-
 /*
 ** Initialize and deinitialize the mutex subsystem.
 */

src/mutex_w32.c

@@ -95,28 +95,6 @@ void sqlite3MemoryBarrier(void){
 #endif
 }
 
-/*
-** Try to provide an atomic compare-and-swap operation on a void pointer,
-** needed for initialization only.
-*/
-void *sqlite3CompareAndSwap(
-  void * volatile *pCurVal,
-  void *cmpVal,
-  void *swapVal
-){
-#if defined(SQLITE_COMPARE_AND_SWAP)
-  return SQLITE_COMPARE_AND_SWAP(pCurVal, cmpVal, swapVal);
-#elif SQLITE_PTRSIZE>4
-  return (void *)InterlockedCompareExchange64(
-      (LONGLONG SQLITE_WIN32_VOLATILE *)pCurVal, (LONGLONG)swapVal,
-      (LONGLONG)cmpVal);
-#else
-  return (void *)InterlockedCompareExchange(
-      (LONG SQLITE_WIN32_VOLATILE *)pCurVal, (LONG)swapVal,
-      (LONG)cmpVal);
-#endif
-}
-
 /*
 ** Initialize and deinitialize the mutex subsystem.
 */

src/sqliteInt.h

@@ -3196,27 +3196,15 @@ const sqlite3_mem_methods *sqlite3MemGetMemsys5(void);
 #ifndef SQLITE_MUTEX_OMIT
   sqlite3_mutex_methods const *sqlite3DefaultMutex(void);
   sqlite3_mutex_methods const *sqlite3NoopMutex(void);
-  void *sqlite3NoopCompareAndSwap(void * volatile *, void *, void *);
   sqlite3_mutex *sqlite3MutexAlloc(int);
   int sqlite3MutexInit(void);
   int sqlite3MutexEnd(void);
 #endif
 #if !defined(SQLITE_MUTEX_OMIT) && !defined(SQLITE_MUTEX_NOOP)
-  void sqlite3MutexCopy(sqlite3_mutex_methods *, sqlite3_mutex_methods const *);
   void sqlite3MemoryBarrier(void);
 #else
-# define sqlite3MutexCopy(x,y)
 # define sqlite3MemoryBarrier()
 #endif
-#if !defined(SQLITE_MUTEX_OMIT)
-# if !defined(SQLITE_MUTEX_NOOP)
-   void *sqlite3CompareAndSwap(void * volatile *, void *, void *);
-# else
-#  define sqlite3CompareAndSwap sqlite3NoopCompareAndSwap
-# endif
-#else
-# define sqlite3CompareAndSwap(x,y,z)
-#endif
 
 sqlite3_int64 sqlite3StatusValue(int);
 void sqlite3StatusUp(int, int);

src/update.c

@@ -496,6 +496,13 @@ void sqlite3Update(
   ** table and index records, and as the values for any new.* references
   ** made by triggers.
   **
+  ** As an optimization, the array is loaded in two passes.  The first pass
+  ** loads unchanged values using OP_Column opcodes so that they can be
+  ** cached and potentially reused by subsequent expressions.  Also, the
+  ** OP_Columns are loaded in reverse order so that the row type/offset cache
+  ** inside the OP_Column implementation in the VDBE will warm up completely
+  ** on the first opcode, rather than incrementally across each opcode.
+  **
   ** If there are one or more BEFORE triggers, then do not populate the
   ** registers associated with columns that are (a) not modified by
   ** this UPDATE statement and (b) not accessed by new.* references. The
@@ -507,25 +514,21 @@ void sqlite3Update(
   newmask = sqlite3TriggerColmask(
       pParse, pTrigger, pChanges, 1, TRIGGER_BEFORE, pTab, onError
   );
-  for(i=0; i<pTab->nCol; i++){
-    if( i==pTab->iPKey ){
-      sqlite3VdbeAddOp2(v, OP_Null, 0, regNew+i);
+  for(i=pTab->nCol-1; i>=0; i--){
+    if( aXRef[i]>=0 && i!=pTab->iPKey ) continue;
+    if( i!=pTab->iPKey
+     && (0==(tmask&TRIGGER_BEFORE) || i>31 || (newmask & MASKBIT32(i))!=0)
+    ){
+      testcase( i==31 );
+      testcase( i==32 );
+      sqlite3ExprCodeGetColumnToReg(pParse, pTab, i, iDataCur, regNew+i);
     }else{
-      j = aXRef[i];
-      if( j>=0 ){
-        sqlite3ExprCode(pParse, pChanges->a[j].pExpr, regNew+i);
-      }else if( 0==(tmask&TRIGGER_BEFORE) || i>31 || (newmask & MASKBIT32(i)) ){
-        /* This branch loads the value of a column that will not be changed 
-        ** into a register. This is done if there are no BEFORE triggers, or
-        ** if there are one or more BEFORE triggers that use this value via
-        ** a new.* reference in a trigger program.
-        */
-        testcase( i==31 );
-        testcase( i==32 );
-        sqlite3ExprCodeGetColumnToReg(pParse, pTab, i, iDataCur, regNew+i);
-      }else{
-        sqlite3VdbeAddOp2(v, OP_Null, 0, regNew+i);
-      }
+      sqlite3VdbeAddOp2(v, OP_Null, 0, regNew+i);
+    }  
+  }
+  for(i=0; i<pTab->nCol; i++){
+    if( (j = aXRef[i])>=0 && i!=pTab->iPKey ){
+      sqlite3ExprCode(pParse, pChanges->a[j].pExpr, regNew+i);
     }
   }
 

src/vdbe.c

@@ -2368,7 +2368,7 @@ case OP_Column: {
   const u8 *zHdr;    /* Next unparsed byte of the header */
   const u8 *zEndHdr; /* Pointer to first byte after the header */
   u32 offset;        /* Offset into the data */
-  u32 szField;       /* Number of bytes in the content of a field */
+  u64 offset64;      /* 64-bit offset */
   u32 avail;         /* Number of bytes of available data */
   u32 t;             /* A type code from the record header */
   u16 fx;            /* pDest->flags value */
@@ -2439,19 +2439,6 @@ case OP_Column: {
     pC->nHdrParsed = 0;
     aOffset[0] = offset;
 
-    /* Make sure a corrupt database has not given us an oversize header.
-    ** Do this now to avoid an oversize memory allocation.
-    **
-    ** Type entries can be between 1 and 5 bytes each.  But 4 and 5 byte
-    ** types use so much data space that there can only be 4096 and 32 of
-    ** them, respectively.  So the maximum header length results from a
-    ** 3-byte type for each of the maximum of 32768 columns plus three
-    ** extra bytes for the header length itself.  32768*3 + 3 = 98307.
-    */
-    if( offset > 98307 || offset > pC->payloadSize ){
-      rc = SQLITE_CORRUPT_BKPT;
-      goto op_column_error;
-    }
 
     if( avail<offset ){
       /* pC->aRow does not have to hold the entire row, but it does at least
@@ -2460,6 +2447,20 @@ case OP_Column: {
       ** dynamically allocated. */
       pC->aRow = 0;
       pC->szRow = 0;
+
+      /* Make sure a corrupt database has not given us an oversize header.
+      ** Do this now to avoid an oversize memory allocation.
+      **
+      ** Type entries can be between 1 and 5 bytes each.  But 4 and 5 byte
+      ** types use so much data space that there can only be 4096 and 32 of
+      ** them, respectively.  So the maximum header length results from a
+      ** 3-byte type for each of the maximum of 32768 columns plus three
+      ** extra bytes for the header length itself.  32768*3 + 3 = 98307.
+      */
+      if( offset > 98307 || offset > pC->payloadSize ){
+        rc = SQLITE_CORRUPT_BKPT;
+        goto op_column_error;
+      }
     }
 
     /* The following goto is an optimization.  It can be omitted and
@@ -2482,11 +2483,8 @@ case OP_Column: {
       /* Make sure zData points to enough of the record to cover the header. */
       if( pC->aRow==0 ){
         memset(&sMem, 0, sizeof(sMem));
-        rc = sqlite3VdbeMemFromBtree(pCrsr, 0, aOffset[0], 
-                                     !pC->isTable, &sMem);
-        if( rc!=SQLITE_OK ){
-          goto op_column_error;
-        }
+        rc = sqlite3VdbeMemFromBtree(pCrsr, 0, aOffset[0], !pC->isTable, &sMem);
+        if( rc!=SQLITE_OK ) goto op_column_error;
         zData = (u8*)sMem.z;
       }else{
         zData = pC->aRow;
@@ -2494,44 +2492,32 @@ case OP_Column: {
   
       /* Fill in pC->aType[i] and aOffset[i] values through the p2-th field. */
       i = pC->nHdrParsed;
-      offset = aOffset[i];
+      offset64 = aOffset[i];
       zHdr = zData + pC->iHdrOffset;
       zEndHdr = zData + aOffset[0];
       assert( i<=p2 && zHdr<zEndHdr );
       do{
-        if( zHdr[0]<0x80 ){
-          t = zHdr[0];
+        if( (t = zHdr[0])<0x80 ){
           zHdr++;
+          offset64 += sqlite3VdbeOneByteSerialTypeLen(t);
         }else{
           zHdr += sqlite3GetVarint32(zHdr, &t);
+          offset64 += sqlite3VdbeSerialTypeLen(t);
         }
-        pC->aType[i] = t;
-        szField = sqlite3VdbeSerialTypeLen(t);
-        offset += szField;
-        if( offset<szField ){  /* True if offset overflows */
-          zHdr = &zEndHdr[1];  /* Forces SQLITE_CORRUPT return below */
-          break;
-        }
-        i++;
-        aOffset[i] = offset;
+        pC->aType[i++] = t;
+        aOffset[i] = (u32)(offset64 & 0xffffffff);
       }while( i<=p2 && zHdr<zEndHdr );
       pC->nHdrParsed = i;
       pC->iHdrOffset = (u32)(zHdr - zData);
-      if( pC->aRow==0 ){
-        sqlite3VdbeMemRelease(&sMem);
-        sMem.flags = MEM_Null;
-      }
+      if( pC->aRow==0 ) sqlite3VdbeMemRelease(&sMem);
   
       /* The record is corrupt if any of the following are true:
       ** (1) the bytes of the header extend past the declared header size
-      **          (zHdr>zEndHdr)
       ** (2) the entire header was used but not all data was used
-      **          (zHdr==zEndHdr && offset!=pC->payloadSize)
       ** (3) the end of the data extends beyond the end of the record.
-      **          (offset > pC->payloadSize)
       */
-      if( (zHdr>=zEndHdr && (zHdr>zEndHdr || offset!=pC->payloadSize))
-       || (offset > pC->payloadSize)
+      if( (zHdr>=zEndHdr && (zHdr>zEndHdr || offset64!=pC->payloadSize))
+       || (offset64 > pC->payloadSize)
       ){
         rc = SQLITE_CORRUPT_BKPT;
         goto op_column_error;
@@ -2550,6 +2536,8 @@ case OP_Column: {
       }
       goto op_column_out;
     }
+  }else{
+    t = pC->aType[p2];
   }
 
   /* Extract the content for the p2+1-th column.  Control can only
@@ -2560,7 +2548,7 @@ case OP_Column: {
   assert( rc==SQLITE_OK );
   assert( sqlite3VdbeCheckMemInvariants(pDest) );
   if( VdbeMemDynamic(pDest) ) sqlite3VdbeMemSetNull(pDest);
-  t = pC->aType[p2];
+  assert( t==pC->aType[p2] );
   if( pC->szRow>=aOffset[p2+1] ){
     /* This is the common case where the desired content fits on the original
     ** page - where the content is not on an overflow page */
@@ -2672,7 +2660,7 @@ case OP_MakeRecord: {
   int file_format;       /* File format to use for encoding */
   int i;                 /* Space used in zNewRecord[] header */
   int j;                 /* Space used in zNewRecord[] content */
-  int len;               /* Length of a field */
+  u32 len;               /* Length of a field */
 
   /* Assuming the record contains N fields, the record format looks
   ** like this:
@@ -2722,8 +2710,7 @@ case OP_MakeRecord: {
   pRec = pLast;
   do{
     assert( memIsValid(pRec) );
-    pRec->uTemp = serial_type = sqlite3VdbeSerialType(pRec, file_format);
-    len = sqlite3VdbeSerialTypeLen(serial_type);
+    pRec->uTemp = serial_type = sqlite3VdbeSerialType(pRec, file_format, &len);
     if( pRec->flags & MEM_Zero ){
       if( nData ){
         if( sqlite3VdbeMemExpandBlob(pRec) ) goto no_mem;

src/vdbeInt.h

@@ -412,7 +412,8 @@ int sqlite3VdbeCursorRestore(VdbeCursor*);
 void sqlite3VdbePrintOp(FILE*, int, Op*);
 #endif
 u32 sqlite3VdbeSerialTypeLen(u32);
-u32 sqlite3VdbeSerialType(Mem*, int);
+u8 sqlite3VdbeOneByteSerialTypeLen(u8);
+u32 sqlite3VdbeSerialType(Mem*, int, u32*);
 u32 sqlite3VdbeSerialPut(unsigned char*, Mem*, u32);
 u32 sqlite3VdbeSerialGet(const unsigned char*, u32, Mem*);
 void sqlite3VdbeDeleteAuxData(Vdbe*, int, int);

src/vdbeaux.c

@@ -2940,11 +2940,13 @@ int sqlite3VdbeCursorMoveto(VdbeCursor *p){
 /*
 ** Return the serial-type for the value stored in pMem.
 */
-u32 sqlite3VdbeSerialType(Mem *pMem, int file_format){
+u32 sqlite3VdbeSerialType(Mem *pMem, int file_format, u32 *pLen){
   int flags = pMem->flags;
   u32 n;
 
+  assert( pLen!=0 );
   if( flags&MEM_Null ){
+    *pLen = 0;
     return 0;
   }
   if( flags&MEM_Int ){
@@ -2958,15 +2960,23 @@ u32 sqlite3VdbeSerialType(Mem *pMem, int file_format){
       u = i;
     }
     if( u<=127 ){
-      return ((i&1)==i && file_format>=4) ? 8+(u32)u : 1;
+      if( (i&1)==i && file_format>=4 ){
+        *pLen = 0;
+        return 8+(u32)u;
+      }else{
+        *pLen = 1;
+        return 1;
+      }
     }
-    if( u<=32767 ) return 2;
-    if( u<=8388607 ) return 3;
-    if( u<=2147483647 ) return 4;
-    if( u<=MAX_6BYTE ) return 5;
+    if( u<=32767 ){ *pLen = 2; return 2; }
+    if( u<=8388607 ){ *pLen = 3; return 3; }
+    if( u<=2147483647 ){ *pLen = 4; return 4; }
+    if( u<=MAX_6BYTE ){ *pLen = 6; return 5; }
+    *pLen = 8;
     return 6;
   }
   if( flags&MEM_Real ){
+    *pLen = 8;
     return 7;
   }
   assert( pMem->db->mallocFailed || flags&(MEM_Str|MEM_Blob) );
@@ -2975,26 +2985,46 @@ u32 sqlite3VdbeSerialType(Mem *pMem, int file_format){
   if( flags & MEM_Zero ){
     n += pMem->u.nZero;
   }
+  *pLen = n;
   return ((n*2) + 12 + ((flags&MEM_Str)!=0));
 }
 
 /*
-** The sizes for serial types less than 12
+** The sizes for serial types less than 128
 */
 static const u8 sqlite3SmallTypeSizes[] = {
-  0, 1, 2, 3, 4, 6, 8, 8, 0, 0, 0, 0
+        /*  0   1   2   3   4   5   6   7   8   9 */   
+/*   0 */   0,  1,  2,  3,  4,  6,  8,  8,  0,  0,
+/*  10 */   0,  0,  0,  0,  1,  1,  2,  2,  3,  3,
+/*  20 */   4,  4,  5,  5,  6,  6,  7,  7,  8,  8,
+/*  30 */   9,  9, 10, 10, 11, 11, 12, 12, 13, 13,
+/*  40 */  14, 14, 15, 15, 16, 16, 17, 17, 18, 18,
+/*  50 */  19, 19, 20, 20, 21, 21, 22, 22, 23, 23,
+/*  60 */  24, 24, 25, 25, 26, 26, 27, 27, 28, 28,
+/*  70 */  29, 29, 30, 30, 31, 31, 32, 32, 33, 33,
+/*  80 */  34, 34, 35, 35, 36, 36, 37, 37, 38, 38,
+/*  90 */  39, 39, 40, 40, 41, 41, 42, 42, 43, 43,
+/* 100 */  44, 44, 45, 45, 46, 46, 47, 47, 48, 48,
+/* 110 */  49, 49, 50, 50, 51, 51, 52, 52, 53, 53,
+/* 120 */  54, 54, 55, 55, 56, 56, 57, 57
 };
 
 /*
 ** Return the length of the data corresponding to the supplied serial-type.
 */
 u32 sqlite3VdbeSerialTypeLen(u32 serial_type){
-  if( serial_type>=12 ){
+  if( serial_type>=128 ){
     return (serial_type-12)/2;
   }else{
+    assert( serial_type<12 
+            || sqlite3SmallTypeSizes[serial_type]==(serial_type - 12)/2 );
     return sqlite3SmallTypeSizes[serial_type];
   }
 }
+u8 sqlite3VdbeOneByteSerialTypeLen(u8 serial_type){
+  assert( serial_type<128 );
+  return sqlite3SmallTypeSizes[serial_type];  
+}
 
 /*
 ** If we are on an architecture with mixed-endian floating 

src/vdbemem.c

@@ -1427,17 +1427,16 @@ static void recordFunc(
   sqlite3_value **argv
 ){
   const int file_format = 1;
-  int iSerial;                    /* Serial type */
+  u32 iSerial;                    /* Serial type */
   int nSerial;                    /* Bytes of space for iSerial as varint */
-  int nVal;                       /* Bytes of space required for argv[0] */
+  u32 nVal;                       /* Bytes of space required for argv[0] */
   int nRet;
   sqlite3 *db;
   u8 *aRet;
 
   UNUSED_PARAMETER( argc );
-  iSerial = sqlite3VdbeSerialType(argv[0], file_format);
+  iSerial = sqlite3VdbeSerialType(argv[0], file_format, &nVal);
   nSerial = sqlite3VarintLen(iSerial);
-  nVal = sqlite3VdbeSerialTypeLen(iSerial);
   db = sqlite3_context_db_handle(context);
 
   nRet = 1 + nSerial + nVal;

test/json101.test

@@ -324,5 +324,22 @@ do_execsql_test json-6.4 {
   SELECT json_valid('["a",55,"b",72]');
 } {1}
 
+# White-space tests.  Note that form-feed is not white-space in JSON.
+# ticket [57eec374ae1d0a1d4a23077a95f4e173fe269113]
+# 
+foreach {tn isvalid ws} {
+  7.1  1  char(0x20)
+  7.2  1  char(0x09)
+  7.3  1  char(0x0A)
+  7.4  1  char(0x0D)
+  7.5  0  char(0x0C)
+  7.6  1  char(0x20,0x09,0x0a,0x0d,0x20)
+  7.7  0  char(0x20,0x09,0x0a,0x0c,0x0d,0x20)
+} {
+  do_execsql_test json-$tn.1 \
+    "SELECT json_valid(printf('%s{%s\"x\"%s:%s9%s}%s',
+         $::ws,$::ws,$::ws,$::ws,$::ws,$::ws));" \
+  $isvalid
+}
 
 finish_test

tool/fuzzershell.c

@@ -726,12 +726,6 @@ int main(int argc, char **argv){
     #ifndef SQLITE_OMIT_TRACE
         sqlite3_trace(db, verboseFlag ? traceCallback : traceNoop, 0);
     #endif
-#ifdef SQLITE_ENABLE_JSON1
-        {
-          extern int sqlite3_json_init(sqlite3*);
-          sqlite3_json_init(db);
-        }
-#endif
         sqlite3_create_function(db, "eval", 1, SQLITE_UTF8, 0, sqlEvalFunc, 0, 0);
         sqlite3_create_function(db, "eval", 2, SQLITE_UTF8, 0, sqlEvalFunc, 0, 0);
         sqlite3_limit(db, SQLITE_LIMIT_LENGTH, 1000000);

tool/vdbe_profile.tcl

@@ -1,8 +1,16 @@
 #!/bin/tclsh
 #
+# SUMMARY:
 # Run this script in the same directory as the "vdbe_profile.out" file.
 # This script summarizes the results contained in that file.
 #
+# DETAILS:
+# Compile SQLite using the -DVDBE_PROFILE option on Linux.  This causes 
+# performance information about individual VDBE operations to be appended
+# to the "vdbe_profile.out" file.  After content has been accumulated in
+# vdbe_profile.out, run this script to analyze the output and generate a
+# report.
+#
 if {![file readable vdbe_profile.out]} {
   error "run this script in the same directory as the vdbe_profile.out file"
 }