Horton

Re: shared-memory based stats collector

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

View thread View on postgr.es
From: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
To: tomas.vondra@2ndquadrant.com
Cc: andres@anarazel.de, ah@cybertec.at, magnus@hagander.net, robertmhaas@gmail.com, tgl@sss.pgh.pa.us, pgsql-hackers@postgresql.org
Date: 2018-11-08T11:46:48Z
Lists: pgsql-hackers

Attachments

Hello. Thank you for looking this.

At Tue, 30 Oct 2018 01:49:59 +0100, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote in <5253d750-890b-069b-031f-2a9b73e47832@2ndquadrant.com>
> Hi,
> 
> I've started looking at the patch over the past few days. I don't have
> any deep insights at this point, but there seems to be some sort of
> issue in pgstat_update_stat. When building using gcc, I do get this
> warning:
> 
> pgstat.c: In function ‘pgstat_update_stat’:
> pgstat.c:648:18: warning: ‘now’ may be used uninitialized in this
> function [-Wmaybe-uninitialized]
>    oldest_pending = now;
>    ~~~~~~~~~~~~~~~^~~~~
> PostgreSQL installation complete.

Uggh! The reason for the code is "last_report = now" comes later
than the code around... Fixed.

> When running this under valgrind, I get a couple of warnings in this
> area of code - see the attached log with a small sample. Judging by
> the locations I assume those are related to the same issue, but I have
> not looked into that.

There was several typos/thinkos related to pointers modifed from
original variables. There was a code like the following in the
original code.

  memset(&shared_globalStats, 0, siazeof(shared_globalStats));

It was not fixed despite this patch changes the type of the
variable from PgStat_GlboalStats to (PgStat_GlobalStats *). As
the result major part of the varialbe remaineduninitialized.

I re-ran this version on valgrind and I didn't see such kind of
problem. Thank you for the testing.



I refactored the patch into complete set consists of 8 files.

v7-0001-sequential-scan-for-dshash.patch
  - dshash sequential scan feature

v7-0002-Add-conditional-lock-feature-to-dshash.patch
  - dshash contitional lock feature

v7-0003-Shared-memory-based-stats-collector.patch
  - Shared memory base stats collector.
    - Remove stats collector process
    - Change stats collector to shared memory base
  (This needs 0004 to work, but it is currently separate from
   this for readability)

v7-0004-Make-archiver-process-an-auxiliary-process.patch
  - Archiver process needs to touch shared memory.
    (I didn't check EXEC_BACKEND case)

v7-0005-Let-pg_stat_statements-not-to-use-PG_STAT_TMP_DIR.patch
  - I removed pg_stat_tmp directory so move pg_stat_statements
    file stored there to pg_stat directory. (This would need fix)

v7-0006-Remove-pg_stat_tmp-exclusion-from-pg_rewind.patch
  - For the same reason with 0005.

v7-0007-Documentation-update.patch
  - Removes description related to pg_stat_tmp.

v7-0008-Split-out-backend-status-monitor-part-from-pgstat.patch
  - Just refactoring. Splits the current postmaster/pgstat.c into
    two files statmon/pgstat.c and statmon/bestatus.c.


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.