mirror of https://github.com/sqlite/sqlite
69 lines
2.2 KiB
Markdown
69 lines
2.2 KiB
Markdown
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## SQLite Expert Extension
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This folder contains code for a simple system to propose useful indexes
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given a database and a set of SQL queries. It works as follows:
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1. The user database schema is copied to a temporary database.
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1. All SQL queries are prepared against the temporary database. The
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**sqlite3\_whereinfo\_hook()** API is used to record information regarding
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the WHERE and ORDER BY clauses attached to each query.
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1. The information gathered in step 2 is used to create (possibly a large
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number of) candidate indexes.
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1. The SQL queries are prepared a second time. If the planner uses any
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of the indexes created in step 3, they are recommended to the user.
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No ANALYZE data is available to the planner in step 4 above. This can lead to sub-optimal results.
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This extension requires that SQLite be built with the
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SQLITE\_ENABLE\_WHEREINFO\_HOOK pre-processor symbol defined.
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# C API
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The SQLite expert C API is defined in sqlite3expert.h. Most uses will proceed
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as follows:
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1. An sqlite3expert object is created by calling **sqlite3\_expert\_new()**.
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A database handle opened by the user is passed as an argument.
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1. The sqlite3expert object is configured with one or more SQL statements
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by making one or more calls to **sqlite3\_expert\_sql()**. Each call may
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specify a single SQL statement, or multiple statements separated by
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semi-colons.
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1. **sqlite3\_expert\_analyze()** is called to run the analysis.
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1. One or more calls are made to **sqlite3\_expert\_report()** to extract
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components of the results of the analysis.
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1. **sqlite3\_expert\_destroy()** is called to free all resources.
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Refer to comments in sqlite3expert.h for further details.
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# sqlite3_expert application
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The file "expert.c" contains the code for a command line application that
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uses the API described above. It can be compiled with (for example):
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<pre>
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gcc -O2 -DSQLITE_ENABLE_WHEREINFO_HOOK sqlite3.c expert.c sqlite3expert.c -o sqlite3_expert
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</pre>
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Assuming the database is "test.db", it can then be run to analyze a single query:
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<pre>
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./sqlite3_expert -sql <sql-query> test.db
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</pre>
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Or an entire text file worth of queries with:
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<pre>
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./sqlite3_expert -file <text-file> test.db
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</pre>
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