Horton

Re: shared-memory based stats collector - v67

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>
Cc: ibrar.ahmad@gmail.com, masao.fujii@oss.nttdata.com, gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2022-03-21T21:30:17Z
Lists: pgsql-hackers

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Hi,

Attached is v67 of the patch. Changes:

- I've committed a number of the earlier patches after polishing them some more
- lots of small cleanups, particularly around reducing unnecessary diff noise
- included Melanie's tests


On 2022-03-17 00:36:52 -0700, Andres Freund wrote:
> I think the first few patches are basically ready to be applied and are
> independently worthwhile:
> - 0001-pgstat-run-pgindent-on-pgstat.c-h.patch
> - 0002-pgstat-split-relation-database-stats-handling-ou.patch
> - 0003-pgstat-split-out-WAL-handling-from-pgstat_-initi.patch
> - 0004-pgstat-introduce-pgstat_relation_should_count.patch
> - 0005-pgstat-xact-level-cleanups-consolidation.patch

Committed.


> Might not be worth having separately, should probably just be part of
> 0014:
> - 0006-pgstat-wip-pgstat-relation-init-assoc.patch

Committed parts, the "assoc" stuff was moved into the main shared memory stats
patch.


> A pain to maintain, needs mostly a bit of polishing of file headers. Perhaps I
> should rename pgstat_checkpoint.c to pgstat_checkpointer.c, fits better with
> function names:
> - 0007-pgstat-split-different-types-of-stats-into-separ.patch

Committed.


> This is also painful to maintain. Mostly kept separate from 0007 for easier
> reviewing:
> - 0009-pgstat-reorder-file-pgstat.c-pgstat.h-contents.patch

Planning to commit this soon (it's now 0001). Doing a last few passes of
readthrough / polishing.


> I don't yet know what we should do with other users of
> PG_STAT_TMP_DIR. There's no need for it for pgstat.c et al anymore. Not sure
> that pg_stat_statement is enough of a reason to keep the stats_temp_directory
> GUC around?
> - 0019-pgstat-wip-remove-stats_temp_directory.patch

Still unclear. Might raise this separately for higher visibility.


> Right now we reset stats for replicas, even if we start from a shutdown
> checkpoint. That seems pretty unnecessary with this patch:
> - 0021-pgstat-wip-only-reset-pgstat-data-after-crash-re.patch

Might raise this in another thread for higher visibility.


> The biggest todos are:
> - Address all the remaining AFIXMEs and XXXs
> - add longer explanation of architecture to pgstat.c (or a README)
> - make naming not "a pain in the neck": [1]
> - lots of polishing
> - run benchmarks - I've done so in the past, but not recently

Still TBD


> - revise docs

Kyotaro-san, maybe you could do a first pass?


> - Further improve our stats test coverage - there's a crapton not covered,
>   despite 0017:
>   - test WAL replay with stats (stats for dropped tables are removed etc)
>   - test crash recovery and "invalid stats file" paths
>   - lot of the pg_stat_ views like bgwriter, pg_stat_database have zero coverage today

That's gotten a lot better with Melanie's tests, still a bit further to go. I
think she's found at least one more small bug that's not yet fixed here.


> - perhaps 0014 can be further broken down - it's still uncomfortably large

Things that I think can be split out:
- Encapsulate "if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)"
  style tests in a helper function. Then just the body needs to be changed,
  rather than a lot of places needing such checks.

Yep, that's it. I don't really see anything else that wouldn't be too
awkward. Would welcome suggestions!.

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.