Hi, On Fri, Jan 24, 2025 at 06:29:46PM +0300, Nazir Bilal Yavuz wrote: > 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.
Yeah I think so (or at least we should document the reason(s) why (and how) they could differ). > I could not > understand the cause of the difference at first glance. I will look > into this and will come back to you. Thanks. > > 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;'. > Thanks for mentioning this filtering! > 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. Yeah. The "init" data was also empty on my side after the pg_stat_reset_shared() and after the insertion in the table. Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
