Adding upstream version 3.40.1.upstream/3.40.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+## SQLite Expert Extension
+
+This folder contains code for a simple system to propose useful indexes
+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.
+     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 candidate 
+     indexes - indexes that the planner might have made use of in the previous
+     step, had they been available.
+
+  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.
+
+# C API
+
+The SQLite expert C API is defined in sqlite3expert.h. Most uses will proceed
+as follows:
+
+  1. An sqlite3expert object is created by calling **sqlite3\_expert\_new()**.
+     A database handle opened by the user is passed as an argument.
+
+  1. The sqlite3expert object is configured with one or more SQL statements
+     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.
+
+  1. One or more calls are made to **sqlite3\_expert\_report()** to extract
+     components of the results of the analysis.
+
+  1. **sqlite3\_expert\_destroy()** is called to free all resources.
+
+Refer to comments in sqlite3expert.h for further details.
+
+# sqlite3_expert application
+
+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 sqlite3.c expert.c sqlite3expert.c -o sqlite3_expert
+</pre>
+
+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
+</pre>
+
+Or an entire text file worth of queries with:
+
+<pre>
+  ./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>