Horton

Re: shared-memory based stats collector - v70

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, 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: 2022-04-06T16:17:51Z
Lists: pgsql-hackers 
Hi,

On 2022-04-06 13:31:31 +0200, Alvaro Herrera wrote:
> Just skimming a bit here ...

Thanks!


> On 2022-Apr-05, Andres Freund wrote:
> 
> > From 0532b869033595202d5797b148f22c61e4eb4969 Mon Sep 17 00:00:00 2001
> > From: Andres Freund <andres@anarazel.de>
> > Date: Mon, 4 Apr 2022 16:53:16 -0700
> > Subject: [PATCH v70 10/27] pgstat: store statistics in shared memory.
> 
> > +      <entry><literal>PgStatsData</literal></entry>
> > +      <entry>Waiting fo shared memory stats data access</entry>
> > +     </row>
> 
> Typo "fo" -> "for"

Oh, oops. I had fixed that in the wrong patch.


> > @@ -5302,7 +5317,9 @@ StartupXLOG(void)
> >  		performedWalRecovery = true;
> >  	}
> >  	else
> > +	{
> >  		performedWalRecovery = false;
> > +	}
> 
> Why? :-)

Damage from merging two commits yesterday. I'd left open where exactly we'd
reset stats, with the "main commit" implementing the current behaviour more
closely, and then a followup commit implementing something a bit
better. Nobody seemed to argue for keeping the behaviour 1:1, so I merged
them. Without removing the parens again :)


> Why give pgstat_get_entry_ref the responsibility of initializing
> created_entry to false?  The vast majority of callers don't care about
> that flag; it seems easier/cleaner to set it to false in
> pgstat_init_function_usage (the only caller that cares that I could
> find) before calling pgstat_prep_pending_entry.

It's annoying to have to initialize it, I agree. But I think it's bugprone for
the caller to know that it has to be pre-initialized to false.


> (I suggest pgstat_prep_pending_entry should have a comment line stating
> "*created_entry, if not NULL, is set true if the entry required to be
> created.", same as pgstat_get_entry_ref.)

Added something along those lines.

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.