Update the README.md file in the ext/expert/ directory.

FossilOrigin-Name: 3b2ff4e0692dfca395d4523b7d5cd0dfd5c319c1072a2a873631fa477cee0b79

ext/expert/README.md

@@ -5,21 +5,20 @@ given a database and a set of SQL queries. It works as follows:
 
   1. The user database schema is copied to a temporary database.
 
-  1. All SQL queries are prepared against the temporary database. The
-     **sqlite3\_whereinfo\_hook()** API is used to record information regarding
-     the WHERE and ORDER BY clauses attached to each query.
+  1. All SQL queries are prepared against the temporary database. I
+     Information regarding the WHERE and ORDER BY clauses, and other query
+     features that affect index selection, are recorded.
 
   1. The information gathered in step 2 is used to create (possibly a large
      number of) candidate indexes.
 
+  1. A subset of the data in the user database is used to generate statistics
+     for all existing indexes and the candidate indexes generated in step 3
+     above.
+
   1. The SQL queries are prepared a second time. If the planner uses any
      of the indexes created in step 3, they are recommended to the user.
 
-No ANALYZE data is available to the planner in step 4 above. This can lead to sub-optimal results.
-
-This extension requires that SQLite be built with the 
-SQLITE\_ENABLE\_WHEREINFO\_HOOK pre-processor symbol defined.
-
 # C API
 
 The SQLite expert C API is defined in sqlite3expert.h. Most uses will proceed
@@ -32,6 +31,10 @@ as follows:
      by making one or more calls to **sqlite3\_expert\_sql()**. Each call may
      specify a single SQL statement, or multiple statements separated by
      semi-colons.
+  
+  1. Optionally, the **sqlite3\_expert\_config()** API may be used to 
+     configure the size of the data subset used to generate index statistics.
+     Using a smaller subset of the data can speed up the analysis.
 
   1. **sqlite3\_expert\_analyze()** is called to run the analysis.
 
@@ -48,10 +51,11 @@ The file "expert.c" contains the code for a command line application that
 uses the API described above. It can be compiled with (for example):
 
 <pre>
-  gcc -O2 -DSQLITE_ENABLE_WHEREINFO_HOOK sqlite3.c expert.c sqlite3expert.c -o sqlite3_expert
+  gcc -O2 sqlite3.c expert.c sqlite3expert.c -o sqlite3_expert
 </pre>
 
-Assuming the database is "test.db", it can then be run to analyze a single query:
+Assuming the database is named "test.db", it can then be run to analyze a
+single query:
 
 <pre>
   ./sqlite3_expert -sql &lt;sql-query&gt; test.db
@@ -63,6 +67,16 @@ Or an entire text file worth of queries with:
   ./sqlite3_expert -file &lt;text-file&gt; test.db
 </pre>
 
+By default, sqlite3_expert generates index statistics using all the data in
+the user database. For a large database, this may be prohibitively time
+consuming. The "-sample" option may be used to configure sqlite3_expert to
+generate statistics based on an integer percentage of the user database as
+follows:
 
+<pre>
+  # Generate statistics based on 25% of the user database rows:
+  ./sqlite3_expert -sample 25 -sql &lt;sql-query&gt; test.db
 
-
+  # Do not generate any statistics at all:
+  ./sqlite3_expert -sample 0 -sql &lt;sql-query&gt; test.db
+</pre>

manifest

@@ -1,5 +1,5 @@
-C Merge\slatest\strunk\schanges\sinto\sthis\sbranch.
-D 2017-04-20T17:35:46.403
+C Update\sthe\sREADME.md\sfile\sin\sthe\sext/expert/\sdirectory.
+D 2017-04-21T19:53:39.781
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