Horton

Re: shared-memory based stats collector

Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>

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From: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
To: andres@anarazel.de
Cc: ah@cybertec.at, magnus@hagander.net, robertmhaas@gmail.com, tgl@sss.pgh.pa.us, pgsql-hackers@postgresql.org
Date: 2018-10-05T08:30:17Z
Lists: pgsql-hackers

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Hello.

At Tue, 02 Oct 2018 16:06:51 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> wrote in <20181002.160651.117284090.horiguchi.kyotaro@lab.ntt.co.jp>
> It doesn't work nor even compile since I failed to include some
> changes. The atached v6-0008 at least compiles and words.
> 
> 0001-0007 are not attached since they are still aplicable on
> master head with offsets.

In this patchset 0001-0007 are still the same with the previous
version. I'll reorganize the whole patchset in the next version.

This is more saner version of previous v5-0008, which didn't pass
regression test. v6-0008 to v6-0010 are attached and they are
applied on top of v5-0001-0007.

- stats collector has been removed.

- modified dshash further so that deletion is allowed during
  sequential scan.

- I'm not sure about the following existing comment at the
  beginning of pgstat.c

  *	- Add a pgstat config column to pg_database, so this
  *	  entire thing can be enabled/disabled on a per db basis.


Some points known to need some considerations are:

1. Concurrency is controlled by per-database entry in db_stats
   dshash. It has 127 lock partitions but all backends on the
   same database share just one lock and only one backend takes
   the right to update stats. (Every backend doesn't update stats
   with the interval not shorter than 500ms, like the current
   stats collector.)  Table-stats can be removed by DROP DB
   simultaeously with stats updates so need to block it using
   per-databsae lock. Any locking means other than dshash might
   be needed.

2. Since dshash cannot allow multiple locks because of resize,
   pgstat_update_stat is forced to be a bit ineffecient.
   It loops onver stats list twice, for shared tables and regular
   tables since we can acquire lock on one database at once.

   Maybe providing individual TabStatusArray for the two will fix
   it, will do in the next version.

3. This adds a new timeout IDLE_STATS_UPDATE_TIMEOUT. This works
   similarly to IDLE_IN_TRANSACTIION_SESSION_TIMEOUT. It fires in
   at most PGSTAT_STAT_MIN_INTERVAL(500)ms to clean up pending
   statistics update.

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.