SQLite will compact these two files into the main file whenever you ordinarily closed all open database connections. Normally you don’t need to care, but if you were to send the database to another machine while your application is running, do not forget to include those two files. Using the WAL journal mode, there will be two additional files next to the database file on your filesystem, which have the same name as the database, but suffixed “-shm” and “-wal”.Setting journal_mode to WAL then improves performance again significantly (approximately 10x or more, depending on the operating system).Īpart from the caveats I already mentioned, you should also be aware of the following: I found that the command PRAGMA synchronous = NORMAL provides a 3-4x speedup. Make sure to read the first few pages to understand what you are doing. Also, there are reduced data consistency guarantees in case of hardware failure. For instance, WAL mode is not available on certain operating systems. However, as documented here, there are a few caveats. The Write-Ahead-Logging (WAL) journal mode significantly improves the write/update performance, compared to the default rollback journal mode. Improve write speed with the Write-Ahead-Log If possible, use the same column in WHERE and ORDER BY, or build a covering index that involves both the WHERE and ORDER BY column.
If you do use such a comparison trick, there is another caveat in case your query contains WHERE and ORDER BY, each with a different column: this will make the query inefficient again. For instance, SQLite evaluates NULL > '' as FALSE. When applying this trick however, make sure you know how SQLite handles NULL comparisons. comparisons involving (greater), or = (equal), but they don’t apply for != (unequal).Ī neat little trick is that you can replace WHERE column != value with WHERE column > value OR column '', because strings are sortable. Indices are only useful if you look for specific values, i.e.
is expensive because SQLite will have to scan all rows of the table, even if the affected column has an index.
Optimize queries that involve IS NOTĬhecking for IS NOT. Use EXPLAIN QUERY PLAN to iterative add or modify your indices until no more SCAN table entries appear. Try to avoid SCAN table entries in the output of EXPLAIN QUERY PLAN whenever possible, because you will run into performance problems on larger databases. lines are a good sign – SQLite uses one of your indices! Take a look at every output line, of which there are three basic variants: As further elaborated by this article, it is a good idea to analyze a query by prefixing it with EXPLAIN QUERY PLAN. The way indices are used internally by SQLite are documented, but not very easy to understand.
Use the query planner to analyze your queries Also, indices only make sense for larger databases, with thousands or millions of rows. The general advice is to create as few indices as possible, but as many as necessary. Unfortunately, indices are a double-edged sword, because they consume additional disk space and they slow down data manipulation ( INSERT, UPDATE, DELETE). Indices also accelerate sorting data ( ORDER BY), or JOINing tables. The basic idea of an index is to speed up reading of specific data, that is, SELECT statements with a WHERE clause. As the following sections will show, there is more to know about SQLite performance tuning than just creating indices. SQLite has a very similar feature set and can also handle millions of rows, given that you know a few tips and tricks about performance tuning. Unlike its bigger, client-server based brothers, such as MySQL, SQLite can be embedded into your application as a library. SQLite is a popular, relational database (DB) system.
Sqlite transaction increased speed update#
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