Horton

Re: shared-memory based stats collector - v67

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: andres@anarazel.de
Cc: melanieplageman@gmail.com, ibrar.ahmad@gmail.com, masao.fujii@oss.nttdata.com, gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2022-03-22T02:56:40Z
Lists: pgsql-hackers 
At Mon, 21 Mar 2022 14:30:17 -0700, Andres Freund <andres@anarazel.de> wrote in 
> Hi,
> 
> Attached is v67 of the patch. Changes:

Thanks for the lot of work on this. 

> > 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.

This looks like committed.

> > 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?

Docs..  Yeah I'll try it.

> > - 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!.

I'm overwhelmed by the amout, but I'm going to look into them.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

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.