Add WAL data to backend statistics
authorMichael Paquier <michael@paquier.xyz>
Tue, 11 Mar 2025 00:04:11 +0000 (09:04 +0900)
committerMichael Paquier <michael@paquier.xyz>
Tue, 11 Mar 2025 00:04:11 +0000 (09:04 +0900)
commit76def4cdd7c2b32d19e950a160f834392ea51744
tree8996570dd7e4c2b4fd9aa9cbffd2fff97ec3fb01
parent59a1592e39fed164d4d6437d62a55aef36e866a5
Add WAL data to backend statistics

This commit adds per-backend WAL statistics, providing the same
information as pg_stat_wal, except that it is now possible to know how
much WAL activity is happening in each backend rather than an overall
aggregate of all the activity.  Like pg_stat_wal, the implementation
relies on pgWalUsage, tracking the difference of activity between two
reports to pgstats.

This data can be retrieved with a new system function called
pg_stat_get_backend_wal(), that returns one tuple based on the PID
provided in input.  Like pg_stat_get_backend_io(), this is useful when
joined with pg_stat_activity to get a live picture of the WAL generated
for each running backend, showing how the activity is [un]balanced.

pgstat_flush_backend() gains a new flag value, able to control the flush
of the WAL stats.

This commit relies mostly on the infrastructure provided by
9aea73fc61d4, that has introduced backend statistics.

Bump catalog version.  A bump of PGSTAT_FILE_FORMAT_ID is not required,
as backend stats do not persist on disk.

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
Discussion: https://postgr.es/m/Z3zqc4o09dM/Ezyz@ip-10-97-1-34.eu-west-3.compute.internal
doc/src/sgml/monitoring.sgml
src/backend/utils/activity/pgstat_backend.c
src/backend/utils/activity/pgstat_wal.c
src/backend/utils/adt/pgstatfuncs.c
src/include/catalog/catversion.h
src/include/catalog/pg_proc.dat
src/include/pgstat.h
src/include/utils/pgstat_internal.h
src/test/regress/expected/stats.out
src/test/regress/sql/stats.sql