Horton

Re: shared-memory based stats collector - v69

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, Justin Pryzby <pryzby@telsasoft.com>, Thomas Munro <thomas.munro@gmail.com>, "David G. Johnston" <david.g.johnston@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2022-04-05T03:05:06Z
Lists: pgsql-hackers

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Hi,

Thanks for the reviews Justin, Thomas, David. I tried to incorporate the
feedback, with the exception of the ongoing discussion around
accessed_across_databases. I've also not renamed pg_stat_exists_stat() yet,
not clear who likes what :)

Changes in v69:

- merged feedback
- committed the first few commits, mostly pretty boring stuff
- added an architecture overview comment to the top of pgstat.c - not sure if
  it makes sense to anybody but me (and perhaps Horiguchi-san)?
- merged "only reset pgstat data after crash recovery." into the main commit,
  added tests verifying the behaviour of not resetting stats on a standby when
  in SHUTDOWNED_IN_RECOVERY.
- drop variable-amount stats when loading on-disk file fails partway through,
  I'd raised this earlier in [1]
- made most pgstat_report_stat() calls pass force = true. In worker.c, the
  only possibly frequent caller, I instead added a pgstat_report_stat(true) to
  the idle path.
- added a handful more tests, but mostly out of "test coverage vanity" ;)
- made the test output of 030_stats_cleanup_replica a bit more informative,
  plus other minor cleanups


The one definite TODO I know of is
> - fix the bug around pgstat_report_stat() I wrote about at [3]
> [3] https://www.postgresql.org/message-id/20220402081648.kbapqdxi2rr3ha3w@alap3.anarazel.de

I'd hoped Horiguchi-san would chime in on that discussion...

Regards,

Andres


[1] https://www.postgresql.org/message-id/20220329191727.mzzwbl7udhpq7pmf%40alap3.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.