Horton

Re: shared-memory based stats collector

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: masao.fujii@oss.nttdata.com, gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2021-04-05T09:29:14Z
Lists: pgsql-hackers

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Hi,

Please find v60 of my version of Horiguchi-san's patch attached. It's now
pretty reasonably split, I think.

Major changes:

- several precursor patches committed

- Split pgstat.c into separate files (see below)

- split into reasonable-ish sized invidual commits, in particular no code is
  moved around in the same commit with function changes

- stats for newly created objects are now dropped on abort

- a good bit of comment, correctness, ... cleanup

- quite a few AFIXME addition denoting places that would need to be fixed
  before commit


I've spent most of the last 2 1/2 weeks on this now. Unfortunately I think
that, while it has gotten a lot closer, it's still about a week's worth of
work away from being committable.

My main concerns are:

- Test Coverage:

  I've added a fair bit of tests, but it's still pretty bad. There were a lot
  of easy-to-hit bugs in earlier versions that nevertheless passed the test
  just fine.

  Due to the addition of pg_stat_force_next_flush(), and that there's no need
  to wait for the stats collector to write out files, it's now a lot more
  realistic to have proper testing of a lot of the pgstat.c code.

- Architectural Review

  I rejiggered the patchset pretty significantly, and I think it needs more
  review than I see as realistic in the next two days. In particular I don't
  think

- Performance Testing

  I did a small amount, but given that this touches just about every query
  etc, I think that's not enough. My changes unfortunately are substantial
  enough to invalidate Horiguchi-san's earlier tests.

- Currently there's a corner case in which function (but not table!)  stats
  for a dropped function may not be removed. That possibly is not too bad,

- Too many FIXMEs still open


It is quite disappointing to not have the patch go into v14 :(. But I just
don't quite see the path right now. But maybe I am just too tired right now,
and it'll look better tomorrow (err today, in a few hours).



On 2021-04-02 10:27:23 -0700, Andres Freund wrote:
> On 2021-04-02 15:34:54 +0900, Kyotaro Horiguchi wrote:
> > At Thu, 1 Apr 2021 19:44:25 -0700, Andres Freund <andres@anarazel.de> wrote in
> > > Hi,
> > >
> > > I spent quite a bit more time working on the patch. There's are large
> > > changes:
> > >
> > > - postmaster/pgstats.c (which is an incorrect location now that it's not
> > >   a subprocess anymore) is split into utils/activity/pgstat.c and
> > >   utils/activity/pgstat_kind.c. I don't love the _kind name, but I
> > >   couldn't come up with anything better.
> >
> > The place was not changed to keep footprint smaller.  I agree that the
> > old place is not appropriate.  pgstat_kind...  How about changin
> > pgstat.c to pgstat_core.c and pgstat_kind.c to pgstat.c?
>
> I don't really like that split over what I chose.

I now changed the split so that there is
utils/activity/pgstat_{database,functions,global,relation}.c

For me that makes the code a lot more readable. Before this change I found it
really hard to know where code should best be put etc, or where to find
code. I found it to be pretty nice to work with after the new split.

The only sad thing about the split is that pgstat_kind_infos now is defined in
pgstat.c, necessitating to expose the callback functions. Seems worth it.

Greetings,

Andres Freund

Commits

  1. Improve comment about dropped entries in pgstat.c

  2. Fix temporary memory leak in system table index scans

  3. pgstat: set timestamps of fixed-numbered stats after a crash.

  4. pgstat: Update docs to match the shared memory stats reality.

  5. pgstat: Hide instability in stats.spec with -DCATCACHE_FORCE_RELEASE.

  6. pgstat: add/extend tests for resetting various kinds of stats.

  7. Add minimal tests for recovery conflict handling.

  8. pgstat: test stats interactions with physical replication.

  9. pgstat: add tests for handling of restarts, including crashes.

  10. pgstat: add tests for transaction behaviour, 2PC, function stats.

  11. pgstat: add pg_stat_have_stats() test helper.

  12. pgstat: add pg_stat_force_next_flush(), use it to simplify tests.

  13. pgstat: move pgstat.c to utils/activity.

  14. pgstat: store statistics in shared memory.

  15. pgstat: remove stats_temp_directory.

  16. pgstat: rename STATS_COLLECTOR GUC group to STATS_CUMULATIVE.

  17. pgstat: revise replication slot API in preparation for shared memory stats.

  18. pgstat: scaffolding for transactional stats creation / drop.

  19. pgstat: introduce PgStat_Kind enum.

  20. pgstat: prepare APIs used by pgstatfuncs for shared memory stats.

  21. pgstat: add pgstat_copy_relation_stats().

  22. pgstat: rename some pgstat_send_* functions to pgstat_report_*.

  23. pgstat: stats collector references in comments.

  24. pgstat: move transactional code into pgstat_xact.c.

  25. dsm: allow use in single user mode.

  26. dshash: revise sequential scan support.

  27. pgstat: remove some superflous comments from pgstat.h.

  28. pgstat: reorder pgstat.[ch] contents.

  29. pgstat: split different types of stats into separate files.

  30. pgstat: introduce pgstat_relation_should_count().

  31. pgstat: separate "xact level" handling out of relation specific functions.

  32. pgstat: rename pgstat_initstats() to pgstat_relation_init().

  33. pgstat: split out WAL handling from pgstat_{initialize,report_stat}.

  34. pgstat: run pgindent on pgstat.c/h.

  35. pgstat: split relation, database handling out of pgstat_report_stat().

  36. Move code around in StartupXLOG().

  37. pgstat: Prepare to use mechanism for truncated rels also for droppped rels.

  38. pgstat: Split out relation stats handling from AtEO[Sub]Xact_PgStat() etc.

  39. pgstat: Schedule per-backend pgstat shutdown via before_shmem_exit().

  40. Schedule ShutdownXLOG() in single user mode using before_shmem_exit().

  41. Make parallel worker shutdown complete entirely via before_shmem_exit().

  42. pgstat: Bring up pgstat in BaseInit() to fix uninitialized use of pgstat by AV.

  43. pgstat: split reporting/fetching of bgwriter and checkpointer stats.

  44. Split backend status and progress related functionality out of pgstat.c.

  45. Split wait event related code from pgstat.[ch] into wait_event.[ch].

  46. Make archiver process an auxiliary process.

  47. Force to send remaining WAL stats to the stats collector at walwriter exit.

  48. Add pg_stat_database counters for sessions and session time

  49. Collect statistics about SLRU caches

  50. Don't run atexit callbacks in quickdie signal handlers.

  51. Create a "fast path" for acquiring weak relation locks.