Horton

Re: shared-memory based stats collector - v68

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: melanieplageman@gmail.com, ibrar.ahmad@gmail.com, masao.fujii@oss.nttdata.com, gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2022-04-04T04:15:16Z
Lists: pgsql-hackers

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Hi,

New version of the shared memory stats patchset. Most important changes:

- It's now "cumulative statistics system", as discussed at [1]. This basically
  is now the term that all the references to the "stats collector" are
  replaced with. Looks much better than "activity statistics" imo. The
  STATS_COLLECTOR is now named STATS_CUMULATIVE.  I tried to find all
  references to either collector or "activity statistics", but in all
  likelihood I didn't get them all.

- updated docs (significantly edited version of the version Kyotaro posted a
  few days ago)

- significantly improved test coverage - pgstat*.c are nearly completely
  covered. While pgstatsfuncs.c coverage has increased, it is not great - but
  there's already so much more coverage, that I think it's good enough for
  now. Thanks to Melanie for help with this!

- largely cleaned up inconsisten function / type naming. Everything now /
  again is under the PgStats_ prefix, except for statistics in shared memory,
  which is prefixed with PgStatsShared_.  I think we should go further and
  add at least a PgStatsPending_ namespace, but that requires touching plenty
  code that didn't need to be touched so far, so it'll have to be task for
  another release.

- As discussed in [2] I added a patch at the start of the queue to clean up
  the inconsistent function header comments conventions.

- pgstat.c is further split. Two new files: pgstat_xact.c and pgstat_shmem.c
  (wrote an email about this a few days ago, without sending the patches)

- Split out as much as I could into separate commits.

- Cleaned up autovacuum.c changes - mostly removing more obsolted code

- code, comment polishing



Still todo:
- docs need review
- finish writing architectural comment atop pgstat.c
- fix the bug around pgstat_report_stat() I wrote about at [3]
- collect who reviewed earlier revisions
- choose what conditions for stats file reset we want
- I'm wondering if the solution for replication slot names on disk is too
  narrow, and instead we should have a more general "serialize" /
  "deserialize" callback. But we can easily do that later as well...


There's a bit more inconsistency around function naming. Right now all
callbacks are pgstat_$kind_$action_cb, but most of the rest of pgstat is
pgstat_$action_$kind.  But somehow it "feels" wrong for the callbacks -
there's also a bunch of functions already named similarly, but that's
partially my fault in commits in the past.


There are a lot of copies of "Permission checking for this function is managed
through the normal GRANT system." in the pre-existing code. Aren't they
completely bogus? None of the functions commented upon like that is actually
exposed to SQL!


Please take a look!


Greetings,

Andres Freund

[1] https://www.postgresql.org/message-id/20220308205351.2xcn6k4x5yivcxyd%40alap3.anarazel.de
[2] https://www.postgresql.org/message-id/20220329191727.mzzwbl7udhpq7pmf%40alap3.anarazel.de
[3] https://www.postgresql.org/message-id/20220402081648.kbapqdxi2rr3ha3w@alap3.anarazel.de

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.