Horton

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

Melanie Plageman <melanieplageman@gmail.com>

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From: Melanie Plageman <melanieplageman@gmail.com>
To: Maciek Sakrejda <m.sakrejda@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, 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>
Date: 2022-10-26T17:54:44Z
Lists: pgsql-hackers

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okay, so I realized v35 had an issue where I wasn't counting strategy
evictions correctly. fixed in attached v36. This made me wonder if there
is actually a way to add a test for evictions (in strategy and shared
contexts) that is not flakey.

On Sun, Oct 23, 2022 at 6:48 PM Maciek Sakrejda <m.sakrejda@gmail.com> wrote:
>
> On Thu, Oct 20, 2022 at 10:31 AM Andres Freund <andres@anarazel.de> wrote:
> > - "repossession" is a very unintuitive name for me. If we want something like
> >   it, can't we just name it reuse_failed or such?
>
> +1, I think "repossessed" is awkward. I think "reuse_failed" works,
> but no strong opinions on an alternate name.

Also, re: repossessed, I can change it to reuse_failed but I do think it
is important to give users a way to distinguish between bulkread
rejections of dirty buffers and strategies failing to reuse buffers due
to concurrent pinning (since the reaction to these two scenarios would
likely be different).

If we added another column called something like "claim_failed" which
counts buffers which we failed to reuse because of concurrent pinning or
usage, we could recommend use of this column together with
"reuse_failed" to determine the cause of the failed reuses for a
bulkread. We could also use "claim_failed" in IOContext shared to
provide information on shared buffer contention.

- Melanie

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.