Horton

Re: shared-memory based stats collector

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, michael@paquier.xyz, thomas.munro@gmail.com, tomas.vondra@2ndquadrant.com, andres@anarazel.de, a.zakirov@postgrespro.ru, ah@cybertec.at, magnus@hagander.net, robertmhaas@gmail.com, pgsql-hackers@postgresql.org
Date: 2020-03-09T18:37:05Z
Lists: pgsql-hackers 
Tom Lane escribió:

In patch 0003,

>  		/*
> -		 * Was it the archiver?  If so, just try to start a new one; no need
> -		 * to force reset of the rest of the system.  (If fail, we'll try
> -		 * again in future cycles of the main loop.).  Unless we were waiting
> -		 * for it to shut down; don't restart it in that case, and
> -		 * PostmasterStateMachine() will advance to the next shutdown step.
> +		 * Was it the archiver?  Normal exit can be ignored; we'll start a new
> +		 * one at the next iteration of the postmaster's main loop, if
> +		 * necessary. Any other exit condition is treated as a crash.
>  		 */
>  		if (pid == PgArchPID)
>  		{
>  			PgArchPID = 0;
>  			if (!EXIT_STATUS_0(exitstatus))
> -				LogChildExit(LOG, _("archiver process"),
> -							 pid, exitstatus);
> -			if (PgArchStartupAllowed())
> -				PgArchPID = pgarch_start();
> +				HandleChildCrash(pid, exitstatus,
> +								 _("archiver process"));
>  			continue;
>  		}

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.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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.