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: magnus@hagander.net, masao.fujii@oss.nttdata.com, gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2021-03-15T08:46:58Z
Lists: pgsql-hackers 
At Sat, 13 Mar 2021 10:05:21 -0800, Andres Freund <andres@anarazel.de> wrote in 
> Hi,
> 
> On 2021-03-13 12:53:30 +0100, Magnus Hagander wrote:
> > On Sat, Mar 13, 2021 at 7:20 AM Andres Freund <andres@anarazel.de> wrote:
> > >    I think before making things differently complicated with this patch,
> > >    we need to clean this up, unfortunately. I think we should initially have
> > >    - src/backend/postmaster/pgstat.c, for a), b) above
> > >    - src/backend/utils/activity/backend_status.c for c)
> > >    - src/backend/utils/activity/wait_events.c for d)
> > >    - src/backend/utils/activity/progress.c for e)
> > >
> > >    Not at all sure about the names, but something roughly like this
> > >    would im make sense.
> > 
> > +1, definitely.
> 
> Cool. I think I can introduce them without causing too much breakage in
> the shmstats patch.

Previously the patch split pgstat.c into pgstat.c and besomething.c
but that was rejected for large footprint. Of course I happily agree
to split (a,b) and c. And also agree to split out d and e.

> Without yet having done it, I think I'd not touch the function name
> prefixes during the move and leave the prototypes in the pgstat.h
> header? Then we could split the header off in a second step (with
> backward compat includes in pgstat.h), potentially combined with a
> rename?  But I'm happy to consider different approaches.

That sounds reasonable. (I did split the header files at the time.)

> > I've been thinking in these lines more than once when poking at
> > differen patches around that area, but they've never been big enough
> > to justify the restructuring on their own. Which then of course just
> > helps accumulate the problem...
> 
> Yea...

^^;

> > If anything, I'd even consider splitting (a) and (b) above out into
> > separate ones as well. But hey, I see you got to that in your next
> > paragraph :)
> 
> I wondered about doing that as a preceding step as well, but it seems a
> bit pointless if all that code needs to be moved elsewhere, and little
> of it survives unchanged...
> 
> 
> > > The next thing to note is that after this whole patchseries, having the
> > > remaining functionality in src/backend/postmaster/pgstat.c doesn't make
> > > sense. The things in postmaster/ are related to postmaster
> > > sub-processes, not random pieces of backend infrastructure. Therefore I
> > > am thinking that patch 0004 should be changed so it basically adds all
> > > the changed code to two new files:
> > > - src/backend/utils/activity/stats.c - for the stats keeping
> > >   infrastructure (shared memory hash table, pending table, etc)
> > > - src/backend/utils/activity/stats_report.c - for pgstat_report_*,
> > >   pgstat_count_*, pgstat_update_*, flush_*, i.e. everything that knows
> > >   about specific kinds of stats.
> > >
> > > The reason for that split is that imo the two pieces of code are largely
> > > independent. One shouldn't need to understand the way stats are stored
> > > in any sort of detail to add a new stats field and vice versa.
> > 
> > Agreed as well.

FWIW, agreed, too.

> Cool. I'll give it a try.


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.