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Add wal_fpi_bytes to pg_stat_wal and pg_stat_get_backend_wal()

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This new counter, called "wal_fpi_bytes", tracks the total amount in
bytes of full page images (FPIs) generated in WAL.  This data becomes
available globally via pg_stat_wal, and for backend statistics via
pg_stat_get_backend_wal().

Previously, this information could only be retrieved with pg_waldump or
pg_walinspect, which may not be available depending on the environment,
and are expensive to execute.  It offers hints about how much FPIs
impact the WAL generated, which could be a large percentage for some
workloads, as well as the effects of wal_compression or page holes.

Bump catalog version.
Bump PGSTAT_FILE_FORMAT_ID, due to the addition of wal_fpi_bytes in
PgStat_WalCounters.

Author: Shinya Kato <shinya11.kato@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAOzEurQtZEAfg6P0kU3Wa-f9BWQOi0RzJEMPN56wNTOmJLmfaQ@mail.gmail.com
This commit is contained in:
Michael Paquier
2025-10-28 16:21:51 +09:00
parent 3e8e05596a
commit f9a09aa295
12 changed files with 46 additions and 15 deletions
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9
doc/src/sgml/monitoring.sgml
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@@ -3323,6 +3323,15 @@ description | Waiting for a newly initialized WAL file to reach durable storage
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>wal_fpi_bytes</structfield> <type>numeric</type>
</para>
<para>
Total amount of WAL full page images in bytes
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>wal_buffers_full</structfield> <type>bigint</type>