Horton

Re: shared-memory based stats collector

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Cc: andres@anarazel.de, ah@cybertec.at, magnus@hagander.net, robertmhaas@gmail.com, tgl@sss.pgh.pa.us, pgsql-hackers@postgresql.org
Date: 2018-11-08T15:06:49Z
Lists: pgsql-hackers 

On 11/8/18 12:46 PM, Kyotaro HORIGUCHI wrote:
> 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.
> 

OK, regression tests now seem to pass without any valgrind issues.

However a quite a few extensions in contrib seem are broken now. It 
seems fixing it is as simple as including the new bestatus.h next to 
pgstat.h.

I'm not sure splitting the headers like this is needed, actually. It's 
true we're replacing pgstat.c with something else, but it's still 
related to stats, backing pg_stat_* system views etc. So I'd keep as 
much of the definitions in pgstat.h, so that it's enough to include that 
one header file. That would "unbreak" the extensions.

Renaming pgstat_report_* functions to bestatus_report_* seems 
unnecessary to me too. The original names seem quite fine to me.

BTW the updated patches no longer apply cleanly. Apparently it got 
broken since Tuesday, most likely by the pread/pwrite patch.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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.