84 lines
3.0 KiB
Markdown
84 lines
3.0 KiB
Markdown
|
## 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 <sql-query> test.db
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
Or an entire text file worth of queries with:
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
./sqlite3_expert -file <text-file> 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 <sql-query> test.db
|
||
|
|
|
||
|
|
# Do not generate any statistics at all:
|
||
|
|
./sqlite3_expert -sample 0 -sql <sql-query> test.db
|
||
|
|
</pre>
|