Horton

Re: shared-memory based stats collector

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: andres@anarazel.de
Cc: masao.fujii@oss.nttdata.com, gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2021-03-12T05:32:52Z
Lists: pgsql-hackers 
At Thu, 11 Mar 2021 19:22:57 -0800, Andres Freund <andres@anarazel.de> wrote in 
> Hi,
> 
> On 2021-03-10 20:26:56 -0800, Andres Freund wrote:
> > > +static void
> > > +attach_shared_stats(void)
> > > +{
> > > +	MemoryContext oldcontext;
> > 
> > > +	/*
> > > +	 * The first attacher backend may still reading the stats file, or the
> > > +	 * last detacher may writing it. Wait for the work to finish.
> > > +	 */
> > 
> > I still believe this kind of approach is too complicated, and we should
> > simply not do any of this "first attacher" business. Instead read it in
> > the startup process or such.
> 
> I started changing the patch to address my complaints. I'll try to do
> it as an incremental patch ontop of your 0004, but it might become too
> unwieldy. Not planning to touch other patches for now (and would be

Sorry for bothering you by that but thank you very much for the
labor. Actually the startup is always the first and lonely attacher
but the last detacher may be any of checkpointer, archiver or
walsender. And I was reluctant to add new stats-mechanism initializer
other than attach_sahred_stats. Those are the reason (to me) for the
*first* attacher mechanism.

However, surely we can separate the "first attacher business" as a
separate function.  And maybe the "fear" backing the complexity is
groundless and such overlap might not actually happen.

The current mechanism repeats read->write process twice while starting
up server, which is annoyance to me.

> happy if the first few were committed).  I do think we'll have to
> split 0004 a bit - it's just too large to commit as is, I think.

Deeply agreed. 0004 is too large and quite confusive to diff.  It is
always tough to resolve a conflict:(

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.