Horton

Re: shared-memory based stats collector - v70

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: "David G. Johnston" <david.g.johnston@gmail.com>
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: 2022-04-06T23:12:09Z
Lists: pgsql-hackers 
Hi,

On 2022-04-06 15:32:39 -0700, David G. Johnston wrote:
> On Wednesday, April 6, 2022, Andres Freund <andres@anarazel.de> wrote:
> 
> >
> >
> > I'd go for
> > pgstat_reset_slru_counter() -> pgstat_reset_slru()
> > pgstat_reset_subscription_counter() -> pgstat_reset_subscription()
> > pgstat_reset_subscription_counters() -> pgstat_reset_all_subscriptions()
> > pgstat_reset_replslot_counter() -> pgstat_reset_replslot()
> > pgstat_reset_replslot_counters() -> pgstat_reset_all_replslots()
> 
> 
> 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.

I'd like to remove the NULL -> all behaviour, but that should be discussed
separately.


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.


> > Not quite sure what to do with pgstat_reset_single_counter(). I'd either go
> > for the minimal pgstat_reset_single_counters() or pgstat_reset_one()?
> >
> 
> Why not add both pgstat_resert_function() and pgstat_reset_table() (to keep
> the pairing) and they can call the renamed pgstat_reset_function_or_table()
> internally (since the function indeed handle both paths and we’ve yet to
> come up with a label to use instead of “function and table stats”)?
> 
> These are private functions right?

What does "private" mean for you? They're exposed via pgstat.h not
pgstat_internal.h. But not to SQL.

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.