Horton

Re: shared-memory based stats collector - v67

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: 2022-03-23T17:42:03Z
Lists: pgsql-hackers 
Hi,

On 2022-03-23 17:27:50 +0900, Kyotaro Horiguchi wrote:
> At Mon, 21 Mar 2022 14:30:17 -0700, Andres Freund <andres@anarazel.de> wrote in 
> > > Right now we reset stats for replicas, even if we start from a shutdown
> > > checkpoint. That seems pretty unnecessary with this patch:
> > > - 0021-pgstat-wip-only-reset-pgstat-data-after-crash-re.patch
> > 
> > Might raise this in another thread for higher visibility.
> 
> +	/*
> +	 * When starting with crash recovery, reset pgstat data - it might not be
> +	 * valid. Otherwise restore pgstat data. It's safe to do this here,
> +	 * because postmaster will not yet have started any other processes
> +	 *
> +	 * TODO: With a bit of extra work we could just start with a pgstat file
> +	 * associated with the checkpoint redo location we're starting from.
> +	 */
> +	if (ControlFile->state == DB_SHUTDOWNED ||
> +		ControlFile->state == DB_SHUTDOWNED_IN_RECOVERY)
> +		pgstat_restore_stats();
> +	else
> +		pgstat_discard_stats();
> +
> 
> Before there, InitWalRecovery changes the state to
> DB_IN_ARCHIVE_RECOVERY if it was either DB_SHUTDOWNED or
> DB_IN_PRODUCTION. So the stat seems like always discarded on standby.

Hm. I though it worked at some point. I guess there's a reason this commit is
a separate commit marked WIP ;)


> In the first place, I'm not sure it is valid that a standby from a
> cold backup takes over the stats from the primary.

I don't really see a reason not to use the stats in that case - we have a
correct stats file after all. But it doesn't seem too important. What I
actually find worth addressing is the case of standbys starting in
DB_SHUTDOWNED_IN_RECOVERY. Right now we always throw stats away after a
*graceful* restart of a standby, which doesn't seem great.

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.