Horton

Re: shared-memory based stats collector - v70

Anton A. Melnikov <a.melnikov@postgrespro.ru>

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From: "Anton A. Melnikov" <a.melnikov@postgrespro.ru>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Michael Paquier <michael@paquier.xyz>
Cc: Andres Freund <andres@anarazel.de>, "Drouvot, Bertrand" <bdrouvot@amazon.com>, Greg Stark <stark@mit.edu>, Tom Lane <tgl@sss.pgh.pa.us>, Melanie Plageman <melanieplageman@gmail.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Thomas Munro <thomas.munro@gmail.com>, "David G. Johnston" <david.g.johnston@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2024-12-10T07:44:29Z
Lists: pgsql-hackers

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Hi!

On 09.12.2024 11:03, Bertrand Drouvot wrote:

> There is a missing space. I think that should be " at server..." or "...%llu ".

Thanks for pointing this out. In the other code the elog messages are all on one line,
regardless of their length. Did the same in v3.

On 10.12.2024 09:42, Bertrand Drouvot wrote:
> On Tue, Dec 10, 2024 at 09:54:36AM +0900, Michael Paquier wrote:
>> On Mon, Dec 09, 2024 at 08:03:54AM +0000, Bertrand Drouvot wrote:
>>> Right. OTOH I think that could help the tap test added in da99fedf8c to not
>>> rely on assert enabled build (the tap test could "simply" check for the
>>> WARNING in the logfile instead).
>>
>> That's true.  Still, the coverage that we have is also enough for
>> assert builds, which is what the test is going to run with most of the
>> time anyway.
> 
> Yeah, that's fine by me and don't see the added value of the WARNING then.

Agreed that this WARNING has no additional value for testing purposes
at pgfarm or ci. Assert is better.
My logic was different.
It's clear that during normal server operation this code should be unreachable.
But we admit that in production deployments it can be executed in case of some bug
that is still unknown to us. Now it is done in such a way that in this case
the server simply skip it and won't notice about it. And no one will know that this happened.
But if there is a warning here, the information will remain in the server logs,
we can find out about it and we can try to reproduce similar behavior
in the testing environment and probably detect a hidden bug like in [1].

Thanks a lot for fixing this!


With the best regards,

-- 
Anton A. Melnikov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

[1] https://www.postgresql.org/message-id/56bf8ff9-dd8c-47b2-872a-748ede82af99%40postgrespro.ru

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.