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: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Andres Freund <andres@anarazel.de>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Magnus Hagander <magnus@hagander.net>, Pg Hackers <pgsql-hackers@postgresql.org>, Lukas Fittl <lukas@fittl.com>, Thomas Munro <thomas.munro@gmail.com>
Date: 2021-09-30T21:16:34Z
Lists: pgsql-hackers

Attachments

On Wed, Sep 29, 2021 at 4:46 PM Melanie Plageman
<melanieplageman@gmail.com> wrote:
>
> On Mon, Sep 27, 2021 at 2:58 PM Melanie Plageman
> <melanieplageman@gmail.com> wrote:
> >
> > On Fri, Sep 24, 2021 at 5:58 PM Melanie Plageman
> > <melanieplageman@gmail.com> wrote:
> > >
> > > On Thu, Sep 23, 2021 at 5:05 PM Melanie Plageman
> > > <melanieplageman@gmail.com> wrote:
> > > The only remaining TODOs are described in the commit message.
> > > most critical one is that the reset message doesn't work.
> >
> > v10 is attached with updated comments and some limited code refactoring
>
> v11 has fixed the oversize message issue by sending a reset message for
> each backend type. Now, we will call GetCurrentTimestamp
> BACKEND_NUM_TYPES times, so maybe I should add some kind of flag to the
> reset message that indicates the first message so that all the "do once"
> things can be done at that point.
>
> I've also fixed a few style/cosmetic issues and updated the commit
> message with a link to the thread [1] where I proposed smgrwrite() and
> smgrextend() wrappers (which is where I propose to call
> pgstat_incremement_buffer_access_type() for unbuffered writes and
> extends).
>
> - Melanie
>
> [1] https://www.postgresql.org/message-id/CAAKRu_aw72w70X1P%3Dba20K8iGUvSkyz7Yk03wPPh3f9WgmcJ3g%40mail.gmail.com


v12 (attached) has various style and code clarity updates (it is
pgindented as well). I also added a new commit which creates a utility
function to make a tuplestore for views that need one in pgstatfuncs.c.

Having received some offlist feedback about the names BufferAccessType
and BufferType being confusing, I am planning to rename these variables
and all of the associated functions. I agree that BufferType and
BufferAccessType are confusing for the following reasons:
  - They sound similar.
  - They aren't very precise.
  - One of the types of buffers is not using a Postgres buffer.

So far, the proposed alternative is IO_Op or IOOp for BufferAccessType
and IOPath for BufferType.

- 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.