Horton

Re: shared-memory based stats collector

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Magnus Hagander <magnus@hagander.net>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Fujii Masao <masao.fujii@oss.nttdata.com>, Georgios <gkokolatos@protonmail.com>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-16T19:08:39Z
Lists: pgsql-hackers 
On Mon, Mar 15, 2021 at 10:56 PM Andres Freund <andres@anarazel.de> wrote:
> I did roughly the first steps of the split as I had outlined. I moved:
>
> 1) wait event related functions into utils/activity/wait_event.c /
>    wait_event.h
>
> 2) "backend status" functionality (PgBackendStatus stuff) into
>    utils/activity/backend_status.c
>
> 3) "progress" related functionality into
>    utils/activity/backend_progress.c

In general, I like this. I'm not too sure about the names. I realize
you don't want to have functions called status.c and progress.c,
because that's awful generic, but now you have backend_progress.c,
backend_status.c, and wait_event.c, which makes the last one look a
little strange. Maybe command_progress.c instead of
backend_progress.c?

> I think 1 and 2 are good (albeit in need of further polish). I'm a bit
> less sure about 3:
> - There's dependency from backend_status.h to backend_progress.h,
>   because it PGSTAT_NUM_PROGRESS_PARAM etc.

That doesn't seem like a catastrophe.

> - it's a fairly small amount of code

But it's not bad to have it separate.

> - there's potential for confusion, because there's also
>   include/commands/progress.h

That could be merged, perhaps. I think I only created that because I
didn't want to jam too much stuff into pgstat.h. But if it has its own
header then jamming some more stuff in there seems more OK.

> - I'm inclined to leave pgstat_report_{activity, tmpfile, appname,
>   timestamp, ..} alone naming-wise, but to rename pgstat_bestart() to
>   something like pgbestat_start()?

I'd probably rename them e.g. command_progress_start(),
comand_progress_update_param(), etc.

> - I've not gone through all the files that could now remove pgstat.h,
>   replacing it with wait_event.h - I'm thinking it might be worth
>   waiting till just after code freeze with that (there'll new additions,
>   and it's likely to cause conflicts)?

Don't care.

> - backend_status.h needs miscadmin.h, due to BackendType. Imo that's a
>   header we should try to avoid exposing in headers if possible. But
>   right now there's no good place to move BackendType to. So I'd let
>   this slide for now.

Why the concern? miscadmin.h is extremely widely-included already.
Maybe it should be broken up into pieces so that we're not including
so MUCH stuff in a zillion places, but the header that contains the
definition of CHECK_FOR_INTERRUPTS() is always going to be needed in a
ton of spots. Honestly, I wonder why we don't just put that part in
postgres.h. If you're writing any significant amount of code and you
don't have at least one CHECK_FOR_INTERRUPTS() in there, you're
probably doing it wrong.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

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.