Horton

Re: shared-memory based stats collector - v70

David G. Johnston <david.g.johnston@gmail.com>

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From: "David G. Johnston" <david.g.johnston@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, "melanieplageman@gmail.com" <melanieplageman@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Thomas Munro <thomas.munro@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2022-04-07T00:01:17Z
Lists: pgsql-hackers 
On Wed, Apr 6, 2022 at 4:12 PM Andres Freund <andres@anarazel.de> wrote:

>
> On 2022-04-06 15:32:39 -0700, David G. Johnston wrote:
> > On Wednesday, April 6, 2022, Andres Freund <andres@anarazel.de> wrote:
> >
> >
> > I like having the SQL function paired with a matching implementation in
> > this scheme.
>
> It would have gotten things closer than it was before imo. We can't just
> rename the SQL functions, they're obviously exposed API.
>

Right, I meant the naming scheme proposed was acceptable.  Not that I
wanted to change the SQL functions too.

I've hacked up the above, but after doing so I think I found a cleaner
>
approach:
>
> I've introduced:
>
> pgstat_reset_of_kind(PgStat_Kind kind) which works for both fixed and
> variable
> numbered stats. That allows to remove pgstat_reset_subscription_counters(),
> pgstat_reset_replslot_counters(), pgstat_reset_shared_counters().
>
> pgstat_reset(PgStat_Kind kind, Oid dboid, Oid objoid), which removes the
> need
> for pgstat_reset_subscription_counter(),
> pgstat_reset_single_counter().



> pgstat_reset_replslot() is still needed, to do
> the name -> index lookup.
>
> That imo makes a lot more sense than requiring each variable-amount kind to
> have wrapper functions.
>
>
I can see benefits of both, or even possibly combining them.  Absent being
able to point to some other part of the system and saying "it is done this
way there, let's do the same here" I think the details will inform the
decision.  The fact there is just the one outlier here suggests that this
is indeed the better option.



> What does "private" mean for you? They're exposed via pgstat.h not
> pgstat_internal.h. But not to SQL.
>
>
I was thinking specifically of the freedom to rename and not break
extensions.  Namely, are these truly implementation details or something
that, while unlikely to be used by extensions, still constitute an exposed
API?  It was mainly a passing thought, I'm not looking for a crash-course
in how all that works right now.

David J.

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.