Hi, Thanks for looking into this!
On Fri, 24 Jan 2025 at 17:20, Bertrand Drouvot <bertranddrouvot...@gmail.com> wrote: > > I did not look at the code yet but did a few tests. > I can see diff between pg_stat_wal and pg_stat_io, for example: > > " > postgres=# select pg_stat_reset_shared(); > pg_stat_reset_shared > ---------------------- > > (1 row) > > postgres=# insert into bdt select a from generate_series(1,200000) a ; > INSERT 0 200000 > > postgres=# select wal_bytes,stats_reset from pg_stat_wal; > wal_bytes | stats_reset > -----------+------------------------------- > 11800088 | 2025-01-24 14:17:28.507994+00 > (1 row) > > postgres=# select sum(write_bytes),stats_reset from pg_stat_io where object = > 'wal' group by stats_reset; > sum | stats_reset > ----------+------------------------------- > 12853248 | 2025-01-24 14:17:28.507988+00 > (1 row) > > Is that expected? I am not sure, I think they need to be the same. I could not understand the cause of the difference at first glance. I will look into this and will come back to you. Quick note: WAL stats in pg_stat_io view includes WAL initialization stats under object = 'wal' and context = 'init', your query may count these initialization stats too. So the correct query is: 'select sum(write_bytes),stats_reset from pg_stat_io where object = 'wal' and context = 'normal' group by stats_reset;'. By saying that, this does not solve the problem; there is still a difference although you omit WAL initialization stats from the pg_stat_io. -- Regards, Nazir Bilal Yavuz Microsoft
