Re: Vacuum statistics

Hi,

On Fri, 2024-09-27 at 11:15 -0700, Masahiko Sawada wrote:
> I'm concerned that a pg_stat_vacuum_tables view has some duplicated
> statistics that we already collect in different ways. For instance,
> total_blks_{read,hit,dirtied,written} are already tracked at
> system-level by pg_stat_io,

pg_stat_vacuum_tables.total_blks_{read,hit,dirtied,written} tracks
blocks used by vacuum in different ways while vacuuming this particular
table while pg_stat_io tracks blocks used by vacuum on the cluster
level.

> and per-relation block I/O statistics can
> be collected using pg_stat_statements.

This is impossible. pg_stat_statements tracks block statistics on a
statement level. One statement could touch many tables and many
indexes, and all used database blocks will be counted by the
pg_stat_statements counters on a statement-level. Autovacuum statistics
won't be accounted by the pg_stat_statements. After all,
pg_stat_statements won't hold the statements statistics forever. Under
pressure of new statements the statement eviction can happen and
statistics will be lost.

All of the above is addressed by relation-level vacuum statistics held
in the Cumulative Statistics System proposed by this patch.
--
regards, Andrei Zubkov
Postgres Professional