931c9701f2
Previously, wal_compression=on was an alias for pglz, with the assumption that users could make an informed choice to pick a better option. But in practice, users rarely got to that second step. Many users don't want to be choosing algorithms - they just want WAL compression, and expect that to work well. The configuration parameter is set by administrators, who do not control the workload, and so are not in a position to evaluate the options anyway. Some users may not even realize there are other options, as previously "on" was the only choice available. This change maps "on" to non-pglz options, supported by the build. Both lz4 and zstd are faster, with a comparable (or better) compression ratio. We prefer zstd over lz4 - per our testing the better compression ratio pays for the lower (de)compression speed. Like for TOAST compression, the value depends on algorithms supported by the PostgreSQL build, with lz4 and zstd being optional. But most builds will have at least one of these external libraries. If neither zstd or lz4 is supported, we fallback to pglz. This only affects what "on" means. Users can still make the informed choice and explicitly select a compression algorithm if it works better for their system. The default value for "wal_compression" remains "off." Initial proposal and patch by wenhui qiu, reviews and patch adjustments by Christoph Berg. A number of other people participated in the discussion. Benchmarks by me. Backpatch to 19. Author: wenhui qiu <qiuwenhuifx@gmail.com> Reviewed-by: Christoph Berg <myon@debian.org> Reviewed-by: Michael Paquier <michael@paquier.xyz> Discussion: https://postgr.es/m/CAGjGUAL1b=Mwd1SCvLbo+fivEr9KDpFcu4jmqKCZXwT=6CiiGQ@mail.gmail.com Backpatch-through: 19
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.