Change wal_compression=on to the first of zstd, lz4, pglz 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 <[email protected]> Reviewed-by: Christoph Berg <[email protected]> Reviewed-by: Michael Paquier <[email protected]> Discussion: https://postgr.es/m/CAGjGUAL1b=Mwd1SCvLbo+fivEr9KDpFcu4jmqKCZXwT=6ci...@mail.gmail.com Backpatch-through: 19 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/931c9701f2509160a2bed7d50129669e2cb32bf9 Modified Files -------------- doc/src/sgml/config.sgml | 12 ++++++------ src/backend/utils/misc/guc_tables.c | 8 ++++---- src/backend/utils/misc/postgresql.conf.sample | 3 ++- src/include/access/xlog.h | 13 +++++++++++++ 4 files changed, 25 insertions(+), 11 deletions(-)
