Horton

Re: shared-memory based stats collector

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: masao.fujii@oss.nttdata.com, gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2021-04-06T16:32:16Z
Lists: pgsql-hackers 
Hi,

On 2021-04-05 02:29:14 -0700, Andres Freund wrote:
> I've spent most of the last 2 1/2 weeks on this now. Unfortunately I think
> that, while it has gotten a lot closer, it's still about a week's worth of
> work away from being committable.
> 
> My main concerns are:
> 
> - Test Coverage:
> 
>   I've added a fair bit of tests, but it's still pretty bad. There were a lot
>   of easy-to-hit bugs in earlier versions that nevertheless passed the test
>   just fine.
> 
>   Due to the addition of pg_stat_force_next_flush(), and that there's no need
>   to wait for the stats collector to write out files, it's now a lot more
>   realistic to have proper testing of a lot of the pgstat.c code.
> 
> - Architectural Review
> 
>   I rejiggered the patchset pretty significantly, and I think it needs more
>   review than I see as realistic in the next two days. In particular I don't
>   think
> 
> - Performance Testing
> 
>   I did a small amount, but given that this touches just about every query
>   etc, I think that's not enough. My changes unfortunately are substantial
>   enough to invalidate Horiguchi-san's earlier tests.
> 
> - Currently there's a corner case in which function (but not table!)  stats
>   for a dropped function may not be removed. That possibly is not too bad,
> 
> - Too many FIXMEs still open
> 
> 
> It is quite disappointing to not have the patch go into v14 :(. But I just
> don't quite see the path right now. But maybe I am just too tired right now,
> and it'll look better tomorrow (err today, in a few hours).
> [...]
> I now changed the split so that there is
> utils/activity/pgstat_{database,functions,global,relation}.c
> 
> For me that makes the code a lot more readable. Before this change I found it
> really hard to know where code should best be put etc, or where to find
> code. I found it to be pretty nice to work with after the new split.

I'm inclined to push patches
[PATCH v60 05/17] pgstat: split bgwriter and checkpointer messages.
[PATCH v60 06/17] pgstat: Split out relation stats handling from AtEO[Sub]Xact_PgStat() etc.
[PATCH v60 09/17] pgstat: xact level cleanups / consolidation.
[PATCH v60 10/17] pgstat: Split different types of stats into separate files.
[PATCH v60 12/17] pgstat: reorder file pgstat.c / pgstat.h contents.

to v14. They're just moving things around, so are fairly low risk. But
they're going to be a pain to maintain. And I think 10 and 12 make
pgstat.c a lot easier to understand.

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.