Add support for zstd with compression of full-page writes in WAL

Enterprise / PostgreSQL - Michael Paquier [] - 11 March 2022 03:18 UTC

wal_compression gains a new value, "zstd", to allow the compression of full-page images using the compression method of the same name.

Compression is done using the default level recommended by the library, as of ZSTD_CLEVEL_DEFAULT = 3. Some benchmarking has shown that it could make sense to use a level lower for the FPI compression, like 1 or 2, as the compression rate did not change much with a bit less CPU consumed, but any tests done would only cover few scenarios so it is hard to come to a clear conclusion. Anyway, there is no reason to not use the default level instead, which is the level recommended by the library so it should be fine for most cases.

zstd outclasses easily pglz, and is better than LZ4 where one wants to have more compression at the cost of extra CPU but both are good enough in their own scenarios, so the choice between one or the other of these comes to a study of the workload patterns and the schema involved, mainly.

This commit relies heavily on 4035cd5, that reshaped the code creating and restoring full-page writes to be aware of the compression type, making this integration straight-forward.

This patch borrows some early work from Andrey Borodin, though the patch got a complete rewrite.

Author: Justin Pryzby Discussion:

e9537321a7 Add support for zstd with compression of full-page writes in WAL
doc/src/sgml/config.sgml | 11 +++++----
doc/src/sgml/installation.sgml | 8 +++++++
src/backend/access/transam/xloginsert.c | 32 ++++++++++++++++++++++++++-
src/backend/access/transam/xlogreader.c | 20 +++++++++++++++++
src/backend/utils/misc/guc.c | 3 +++
src/backend/utils/misc/postgresql.conf.sample | 2 +-
src/bin/pg_waldump/pg_waldump.c | 2 ++
src/include/access/xlog.h | 3 ++-
src/include/access/xlogrecord.h | 5 ++++-
9 files changed, 78 insertions(+), 8 deletions(-)


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