Horton

Re: shared-memory based stats collector

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, michael@paquier.xyz, thomas.munro@gmail.com, tomas.vondra@2ndquadrant.com, a.zakirov@postgrespro.ru, ah@cybertec.at, magnus@hagander.net, robertmhaas@gmail.com, pgsql-hackers@postgresql.org
Date: 2020-03-09T19:25:39Z
Lists: pgsql-hackers 
Hi,

On 2020-03-09 15:04:23 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > On 2020-03-09 15:37:05 -0300, Alvaro Herrera wrote:
> >> I'm worried that we're causing all processes to terminate when an
> >> archiver dies in some ugly way; but in the current coding, it's pretty
> >> harmless and we'd just start a new one.  I think this needs to be
> >> reconsidered.  As far as I know, pgarchiver remains unconnected to
> >> shared memory so a crash-restart cycle is not necessary.  We should
> >> continue to just log the error message and move on.
> 
> > Why is it worth having the archiver be "robust" that way?
> 
> I'd ask a different question: what the heck is this patchset doing
> touching the archiver in the first place?  I can see no plausible
> reason for that doing anything related to stats collection.

As of a release or two back, it sends stats messages for archiving
events:

			if (pgarch_archiveXlog(xlog))
			{
				/* successful */
				pgarch_archiveDone(xlog);

				/*
				 * Tell the collector about the WAL file that we successfully
				 * archived
				 */
				pgstat_send_archiver(xlog, false);

				break;			/* out of inner retry loop */
			}
			else
			{
				/*
				 * Tell the collector about the WAL file that we failed to
				 * archive
				 */
				pgstat_send_archiver(xlog, true);


> If we now need some new background processing for stats, let's make a
> new postmaster child process to do that, not overload the archiver
> with unrelated responsibilities.

I don't think that's what's going on. It's just changing the archiver so
it can report stats via shared memory - which subsequently means that it
needs to deal differently with errors than when it wasn't connected.

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.