Horton

Re: shared-memory based stats collector

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: gkokolatos@protonmail.com
Cc: pgsql-hackers@lists.postgresql.org
Date: 2020-11-06T00:27:56Z
Lists: pgsql-hackers

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At Wed, 04 Nov 2020 17:39:10 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in 
> At Fri, 30 Oct 2020 15:00:55 +0000, Georgios Kokolatos <gkokolatos@protonmail.com> wrote in 
> > Hi,
> > 
> > I noticed that according to the cfbot this patch no longer applies.
> > 
> > As it is registered in the upcoming commitfest, it would be appreciated
> > if you could rebase it.
> 
> Thanks!  The replication slot stats patch (9868167500) hit this.
> 
> - Fixed a bug of original code.
> 
>  get_stat_entry() returned a wrong result to found when shared entry
>  exists but it is not locally cached.
> 
> - Moved replication slot stats into shared memory stats.
> 
>  Differently from wal_stats and slru_stats, it can be implemented as a
>  part of unified stats entry.  I'm tempted to remove the entry for a
>  dropped slot immediately, but I didn't that since the number of the
>  slots should be under 10 or so and dropping an entry requires
>  exclusive lock on dshash.  Instead, dropped entries are removed at
>  file-write time that happens only at the end of a process.
> 
> 
> I had to clean up replication slots in pgstat_beshutdown_hook(). Even
> though we have exactly the same code in several other places, the
> function must be called before disabling DSA because we cannot update
> statistics after detaching the shared-memory stats.  Perhaps we can
> remove some of the existing calling to ReplicationSlotCleanup() but I
> haven't do that in this version.

Fixed a bug that pgstat_report_replslot fails to reuse entries that
are marked as "dropped".

Fixed comments for the caller sites to pgstat_report_replslot(_drop)
in ReplicationSlotCreate() and ReplicationSlotDropPtr().

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

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.