Horton

Re: shared-memory based stats collector

Fujii Masao <masao.fujii@oss.nttdata.com>

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From: Fujii Masao <masao.fujii@oss.nttdata.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, gkokolatos@protonmail.com
Cc: pgsql-hackers@lists.postgresql.org
Date: 2021-03-05T15:32:07Z
Lists: pgsql-hackers 

On 2021/03/05 17:18, Kyotaro Horiguchi wrote:
> At Thu, 21 Jan 2021 12:03:48 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in
>> Commit 960869da08 (database statistics) conflicted with this. Rebased.
>>
>> I'm concerned about the behavior that pgstat_update_connstats calls
>> GetCurrentTimestamp() every time stats update happens (with intervals
>> of 10s-60s in this patch). But I didn't change that design since that
>> happens with about 0.5s intervals in master and the rate is largely
>> reduced in this patch, to make this patch simpler.
> 
> I stepped on my foot, and another commit coflicted. Just rebased.

Thanks for rebasing the patches!

I think that 0003 patch is self-contained and useful, for example which
enables us to monitor archiver process in pg_stat_activity. So IMO
it's worth pusing 0003 patch firstly.

Here are the review comments for 0003 patch.

+	/* Archiver process's latch */
+	Latch	   *archiverLatch;
+	/* Current shared estimate of appropriate spins_per_delay value */

The last line in the above seems not necessary.

In proc.h, NUM_AUXILIARY_PROCS needs to be incremented.

     /* ----------
      * Functions called from postmaster
      * ----------
      */
     extern int	pgarch_start(void);

In pgarch.h, the above is not necessary.

+extern void XLogArchiveWakeup(void);

This seems no longer necessary.

+extern void XLogArchiveWakeupStart(void);
+extern void XLogArchiveWakeupEnd(void);
+extern void XLogArchiveWakeup(void);

These seem also no longer necessary.

  			PgArchPID = 0;
  			if (!EXIT_STATUS_0(exitstatus))
-				LogChildExit(LOG, _("archiver process"),
-							 pid, exitstatus);
-			if (PgArchStartupAllowed())
-				PgArchPID = pgarch_start();
+				HandleChildCrash(pid, exitstatus,
+								 _("archiver process"));

I don't think that we should treat non-zero exit condition as a crash,
as before. Otherwise when archive_command fails on a signal,
archiver emits FATAL error and which leads the server restart.

- * walwriter, autovacuum, or background worker.
+ * walwriter, autovacuum, archiver or background worker.
   *
   * The objectives here are to clean up our local state about the child
   * process, and to signal all other remaining children to quickdie.
@@ -3609,6 +3606,18 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
  		signal_child(AutoVacPID, (SendStop ? SIGSTOP : SIGQUIT));
  	}
  
+	/* Take care of the archiver too */
+	if (pid == PgArchPID)
+		PgArchPID = 0;
+	else if (PgArchPID != 0 && take_action)
+	{
+		ereport(DEBUG2,
+				(errmsg_internal("sending %s to process %d",
+								 (SendStop ? "SIGSTOP" : "SIGQUIT"),
+								 (int) PgArchPID)));
+		signal_child(PgArchPID, (SendStop ? SIGSTOP : SIGQUIT));
+	}
+

Same as above.


In xlogarchive.c, "#include "storage/pmsignal.h"" is no longer necessary.


pgarch_forkexec() should be removed from pgarch.c because it's no longer used.


     /* ------------------------------------------------------------
      * Public functions called from postmaster follow
      * ------------------------------------------------------------
      */

The definition of PgArchiverMain() should be placed just
after the above comment.


exit(0) in PgArchiverMain() should be proc_exit(0)?

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION

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.