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: Andres Freund <andres@anarazel.de>
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: 2023-01-09T21:10:47Z
Lists: pgsql-hackers

Attachments

Attached is v45 of the patchset. I've done some additional code cleanup
and changes. The most significant change, however, is the docs. I've
separated the docs into its own patch for ease of review.

The docs patch here was edited and co-authored by Samay Sharma.
I'm not sure if the order of pg_stat_io in the docs is correct.

The significant changes are removal of all "correspondence" or
"equivalence"-related sections (those explaining how other IO stats were
the same or different from pg_stat_io columns).

I've tried to remove references to "strategies" and "Buffer Access
Strategy" as much as possible.

I've moved the advice and interpretation section to the bottom --
outside of the table of definitions. Since this page is primarily a
reference page, I agree with Samay that incorporating interpretation
into the column definitions adds clutter and confusion.

I think the best course would be to have an "Interpreting Statistics"
section.

I suggest a structure like the following for this section:
    - Statistics Collection Configuration
    - Viewing Statistics
    - Statistics Views Reference
    - Statistics Functions Reference
    - Interpreting Statistics

As an aside, this section of the docs has some other structural issues
as well.

For example, I'm not sure it makes sense to have the dynamic statistics
views as sub-sections under 28.2, which is titled "The Cumulative
Statistics System."

In fact the docs say this under Section 28.2
https://www.postgresql.org/docs/current/monitoring-stats.html

"PostgreSQL also supports reporting dynamic information about exactly
what is going on in the system right now, such as the exact command
currently being executed by other server processes, and which other
connections exist in the system. This facility is independent of the
cumulative statistics system."

So, it is a bit weird that they are defined under the section titled
"The Cumulative Statistics System".

In this version of the patchset, I have not attempted a new structure
but instead moved the advice/interpretation for pg_stat_io to below the
table containing the column definitions.

- 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.