Horton

Re: shared-memory based stats collector

Ibrar Ahmed <ibrar.ahmad@gmail.com>

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From: Ibrar Ahmed <ibrar.ahmad@gmail.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: Georgios Kokolatos <gkokolatos@protonmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Fujii Masao <masao.fujii@oss.nttdata.com>
Date: 2021-03-08T16:55:31Z
Lists: pgsql-hackers 
On Fri, Mar 5, 2021 at 8:32 PM Fujii Masao <masao.fujii@oss.nttdata.com>
wrote:

>
>
> 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
>
>
>
The code does not compile and has compilation warnings and errors.


------
pgstat.c:446:25: note: ‘cached_slrustats’ declared here
static PgStat_SLRUStats cached_slrustats;
^~~~~~~~~~~~~~~~
guc.c:4372:4: error: use of undeclared identifier 'pgstat_temp_directory';
did you mean 'pgstat_stat_directory'?
&pgstat_temp_directory,
^~~~~~~~~~~~~~~~~~~~~
pgstat_stat_directory
../../../../src/include/pgstat.h:922:14: note: 'pgstat_stat_directory'
declared here
extern char *pgstat_stat_directory;
^
guc.c:4373:3: error: use of undeclared identifier 'PG_STAT_TMP_DIR'
PG_STAT_TMP_DIR,
^
guc.c:4374:25: error: use of undeclared identifier
'assign_pgstat_temp_directory'
check_canonical_path, assign_pgstat_temp_directory, NULL

-------


Can we get an updated patch?

I am marking the patch "Waiting on Author"


-- 
Ibrar Ahmed

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.