Horton

Re: shared-memory based stats collector

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, tgl@sss.pgh.pa.us, 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: 2020-03-10T21:32:42Z
Lists: pgsql-hackers 
On 2020-03-10 09:48:07 -0300, Alvaro Herrera wrote:
> On 2020-Mar-10, Kyotaro Horiguchi wrote:
> 
> > At Mon, 9 Mar 2020 20:34:20 -0700, Andres Freund <andres@anarazel.de> wrote in 
> > > On 2020-03-10 12:27:25 +0900, Kyotaro Horiguchi wrote:
> > > > That's true, but I have the same concern with Tom. The archive bacame
> > > > too-tightly linked with other processes than actual relation.
> > > 
> > > What's the problem here? We have a number of helper processes
> > > (checkpointer, bgwriter) that are attached to shared memory, and it's
> > > not a problem.
> > 
> > That theoretically raises the chance of server-crash by a small amount
> > of probability. But, yes, it's absurd to prmise that archiver process
> > crashes.
> 
> The case I'm worried about is a misconfigured archive_command that
> causes the archiver to misbehave (exit with a code other than 0); if
> that already doesn't happen, or we can make it not happen, then I'm okay
> with the changes to archiver.

Well, an exit(1) is also fine, afaict. No?

The archive command can just trigger either a FATAL or a LOG:

	rc = system(xlogarchcmd);
	if (rc != 0)
	{
		/*
		 * If either the shell itself, or a called command, died on a signal,
		 * abort the archiver.  We do this because system() ignores SIGINT and
		 * SIGQUIT while waiting; so a signal is very likely something that
		 * should have interrupted us too.  Also die if the shell got a hard
		 * "command not found" type of error.  If we overreact it's no big
		 * deal, the postmaster will just start the archiver again.
		 */
		int			lev = wait_result_is_any_signal(rc, true) ? FATAL : LOG;

		if (WIFEXITED(rc))
		{
			ereport(lev,
					(errmsg("archive command failed with exit code %d",
							WEXITSTATUS(rc)),
					 errdetail("The failed archive command was: %s",
							   xlogarchcmd)));
		}
		else if (WIFSIGNALED(rc))
		{
#if defined(WIN32)
			ereport(lev,
					(errmsg("archive command was terminated by exception 0x%X",
							WTERMSIG(rc)),
					 errhint("See C include file \"ntstatus.h\" for a description of the hexadecimal value."),
					 errdetail("The failed archive command was: %s",
							   xlogarchcmd)));
#else
			ereport(lev,
					(errmsg("archive command was terminated by signal %d: %s",
							WTERMSIG(rc), pg_strsignal(WTERMSIG(rc))),
					 errdetail("The failed archive command was: %s",
							   xlogarchcmd)));
#endif
		}
		else
		{
			ereport(lev,
					(errmsg("archive command exited with unrecognized status %d",
							rc),
					 errdetail("The failed archive command was: %s",
							   xlogarchcmd)));
		}

		snprintf(activitymsg, sizeof(activitymsg), "failed on %s", xlog);
		set_ps_display(activitymsg, false);

		return false;
	}

I.e. there's only normal ways to shut down the archiver due to a failing
archvie command.

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.