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: tomas.vondra@2ndquadrant.com
Cc: andres@anarazel.de, a.zakirov@postgrespro.ru, alvherre@2ndquadrant.com, ah@cybertec.at, magnus@hagander.net, robertmhaas@gmail.com, tgl@sss.pgh.pa.us, pgsql-hackers@postgresql.org
Date: 2019-05-17T05:27:22Z
Lists: pgsql-hackers

Attachments

Hello.

At Wed, 10 Apr 2019 11:13:27 +0200, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote in <20190410091327.fpnvjbuu74dzxizl@development>
> While reviewing the patch I've always had issue with evaluating how it
> behaves for various scenarios / workloads. The reviews generally did
> one
> specific benchmark, but I find that unsatisfactory. I wonder whether
> if
> we could develop a small set of more comprehensive workloads for this
> patch (i.e. different numbers of objects, access patterns, ...).

Indeed. I'm having difficulty also with catcache pruning
stuff. But I might have found a clue to that.

I took performance numbers after some amendment and polishment of
the patch.

I expected operf might work but it doesn't show meaningful
information with O2'ed binary. gprof slows binary to about one
third. But just running pgbench gave me rather stable numbers
(differently from catcache stuff..).

The numbers are tps for 300 minutes run and ratio between master
and patched.

[A-D]1 are just running stats-updator clients.

      master-O2     patched       patched/master-O2
A1:  13431.603208  13457.968950   100.1963
B1:  72284.737474  72535.169437   100.3465
C1:     19.963315     20.037411   100.3712
D1:    193.027074    196.651603   101.8777


[A-D]2 tests introduces stats-reader client.

          master-O2                patched               patched/master-O2
        updator /  reader       updator /  reader      updator /  reader
A2: 12929.418503/512.784200  13066.150297/584.686889    101.0575 / 114.0220
B2: 71673.804812/ 20.102687  71916.823242/ 22.109251    100.3391 / 109.9816
C2:    16.066719/485.788495     16.487942/577.930340    102.6217 / 118.9675
D2:   189.563306/ 36.252532    193.817075/ 44.661707    102.2440 / 123.1961


Case A1 is most simplest case: 1 client repeatedly updated stats
   of pgbench_acconts (of scale-1, but that doesn't matter)

Case B1 is A1 from 100 concurrent clients.

Case C1 is massive(?) number of stats update: Concretely select
  sum() on a partitioned table with 1000 children, from 1 client.

Case D1 doesn C1 from 97 concurrent clients.

A2-D2 are running a single stats referencing client while A1-D1
are running respectively. (select sum(seq_scan) from pg_stat_user_tables)

Perhaps the number will get worse having many rerefencing clients
but I think it's not realistic.


I'll run test with many databases (-100?) and expanded tabstat
entry cases.

The attached files are:

v19-0001-sequential-scan-for-dshash.patch:
v19-0002-Add-conditional-lock-feature-to-dshash.patch:
v19-0003-Make-archiver-process-an-auxiliary-process.patch:
v19-0005-Remove-the-GUC-stats_temp_directory.patch:

 not changed since v18 except rebasing.

v19-0004-Shared-memory-based-stats-collector.patch:

 Rebased. Fixed several bugs. Improved performance in some
 cases. Made structs/code tidier. Added/rewrote comments.

run.sh   : main test script
gencr.pl : partitioned table generator script generator
           (perl gencr.pl | psql postgres to run)
tr.sql   : stats-updator client script used by run.sh
ref.sql  : stats-reader client script used by run.sh


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.