Horton

Re: pg_stat_bgwriter.buffers_backend is pretty meaningless (and more?)

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Lukas Fittl <lukas@fittl.com>, Justin Pryzby <pryzby@telsasoft.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Magnus Hagander <magnus@hagander.net>, Pg Hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>, Maciek Sakrejda <m.sakrejda@gmail.com>
Date: 2022-12-28T23:56:13Z
Lists: pgsql-hackers 
Hi,

On 2022-10-06 13:42:09 -0400, Melanie Plageman wrote:
> > Additionally, some minor notes:
> >
> > - Since the stats are counting blocks, it would make sense to prefix the view columns with "blks_", and word them in the past tense (to match current style), i.e. "blks_written", "blks_read", "blks_extended", "blks_fsynced" (realistically one would combine this new view with other data e.g. from pg_stat_database or pg_stat_statements, which all use the "blks_" prefix, and stop using pg_stat_bgwriter for this which does not use such a prefix)
>
> I have changed the column names to be in the past tense.

For a while I was convinced by the consistency argument (after Melanie
pointing it out to me). But the more I look, the less convinced I am. The
existing IO related stats in pg_stat_database, pg_stat_bgwriter aren't past
tense, just the ones in pg_stat_statements. pg_stat_database uses past tense
for tup_*, but not xact_*, deadlocks, checksum_failures etc.

And even pg_stat_statements isn't consistent about it - otherwise it'd be
'planned' instead of 'plans', 'called' instead of 'calls' etc.

I started to look at the naming "tense" issue again, after I got "confused"
about "extended", because that somehow makes me think about more detailed
stats or such, rather than files getting extended.

ISTM that 'evictions', 'extends', 'fsyncs', 'reads', 'reuses', 'writes' are
clearer than the past tense versions, and about as consistent with existing
columns.


FWIW, I've been hacking on this code a bunch, mostly around renaming things
and changing the 'stacking' of the patches. My current state is at
https://github.com/anarazel/postgres/tree/pg_stat_io
A bit more to do before posting the edited version...

Greetings,

Andres Freund

Commits

  1. Stabilize pg_stat_io writes test

  2. Fix flakey pg_stat_io test

  3. Suppress more compiler warnings in new pgstats code.

  4. Suppress compiler warnings in new pgstats code.

  5. Add tests for pg_stat_io

  6. Create regress_tblspc in test_setup

  7. Add pg_stat_io view, providing more detailed IO statistics

  8. pgstat: Track more detailed relation IO statistics

  9. pgstat: Infrastructure for more detailed IO statistics

  10. doc: Fix some issues in logical replication section

  11. Manual cleanup and pgindent of pgstat and bufmgr related code

  12. Have the planner consider Incremental Sort for DISTINCT

  13. Use actual backend IDs in pg_stat_get_backend_idset() and friends.

  14. Remove redundant call to pgstat_report_wal()

  15. Add BackendType for standalone backends

  16. Initialize backend status reporting during bootstrap.