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: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, tgl@sss.pgh.pa.us, vignesh21@gmail.com, pryzby@telsasoft.com, lukas@fittl.com, alvherre@alvh.no-ip.org, magnus@hagander.net, pgsql-hackers@postgresql.org, thomas.munro@gmail.com, m.sakrejda@gmail.com
Date: 2023-03-06T19:34:04Z
Lists: pgsql-hackers 
Hi,

On 2023-03-06 14:24:09 -0500, Melanie Plageman wrote:
> On Mon, Mar 06, 2023 at 11:09:19AM -0800, Andres Freund wrote:
> > On 2023-03-06 10:09:24 -0500, Melanie Plageman wrote:
> > > On Mon, Mar 6, 2023 at 1:48 AM Kyotaro Horiguchi
> > > <horikyota.ntt@gmail.com> wrote:
> > > >
> > > > At Mon, 06 Mar 2023 15:24:25 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in
> > > > > In any case, I think we need to avoid such concurrent autovacuum/analyze.
> > > >
> > > > If it is correct, I believe the attached fix works.
> > > 
> > > Thanks for investigating this!
> > > 
> > > Yes, this fix looks correct and makes sense to me.
> > 
> > Wouldn't it be better to just perform the section from the ALTER TABLE till
> > the DROP TABLE in a transaction? Then there couldn't be any other accesses in
> > just that section. I'm not convinced it's good to disallow all concurrent
> > activity in other parts of the test.
> 
> You mean for test coverage reasons? Because the table in question only
> exists for a few operations in this test file.

That, but also because it's simply more reliable. autovacuum=off doesn't
protect against a anti-wraparound vacuum or such. Or a concurrent test somehow
triggering a read. Or ...

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.