Horton

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

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: andres@anarazel.de
Cc: melanieplageman@gmail.com, pryzby@telsasoft.com, alvherre@alvh.no-ip.org, magnus@hagander.net, pgsql-hackers@postgresql.org, lukas@fittl.com, thomas.munro@gmail.com
Date: 2022-07-13T02:41:40Z
Lists: pgsql-hackers 
At Tue, 12 Jul 2022 19:18:22 -0700, Andres Freund <andres@anarazel.de> wrote in 
> Hi,
> 
> On 2022-07-13 11:00:07 +0900, Kyotaro Horiguchi wrote:
> > I imagined to use B_INVALID as a kind of "default" partition, which
> > accepts all unknown backend types.
> 
> There shouldn't be any unknown backend types. Something has gone wrong if we
> get far without a backend type set.
> 
> 
> > We can just ignore that values but then we lose the clue for malfunction of
> > stats machinery. I thought that that backend-type as the sentinel for
> > malfunctions.  Thus we can emit logs instead.
> > 
> > I feel that the stats machinery shouldn't stop the server as possible,
> > or I think it is overreaction to abort for invalid values that can be
> > easily coped with.
> 
> I strongly disagree. That just ends up with hard to find bugs.

I was not sure about the policy on that since, as Melanie (and I)
mentioned, GetBackendTypeDesc() is gracefully treating invalid values.

Since both of you are agreeing on this point, I'm fine with
Assert()ing assuming that GetBackendTypeDesc() (or other places
backend-type is handled) is modified to behave the same way.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

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.