Horton

Re: shared-memory based stats collector

Fujii Masao <masao.fujii@oss.nttdata.com>

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From: Fujii Masao <masao.fujii@oss.nttdata.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: andres@anarazel.de, gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2021-03-12T14:33:05Z
Lists: pgsql-hackers

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On 2021/03/12 17:24, Kyotaro Horiguchi wrote:
> At Fri, 12 Mar 2021 15:13:15 +0900, Fujii Masao <masao.fujii@oss.nttdata.com> wrote in
>> On 2021/03/12 13:49, Kyotaro Horiguchi wrote:
>>> I noticed that I accidentally removed the launch-suppression feature
>>> that is to avoid frequent relaunching.  That mechanism is needed on
>>> the postmaster side. I added PgArchIsSuppressed() to do the same check
>>> with the old pgarch_start() and make it called as a part of
>>> PgArchStartupAllowed().
>>
>> You're right! At least for me the function name PgArchIsSuppressed()
>> sounds not good to me. What about something like PgArchCanRestart()?
> 
> The reason for the name was some positive-meaning names came up with
> me are confusing with PgArchStartupAllowed().  The name
> PgArchCanRestart suggests that it's usable only when
> restarting. However, the function requires to be called also when the
> first launch since last_pgarch_start_time needs to be updated every
> time archiver is launched.
> 
> Anyway in the attached the name is changed wihtout changing its usage.

Thanks! If we come up with better name, let's rename the function later.

> 
> # I don't like it uses "can" as "allowed" so much. The archiver
> # actually can restart but is just inhibited to restart.
> 
>> This is not fault of this patch. But last_pgarch_start_time should be
>> initialized with zero?
> 
> Right. I noticed that but forgot to fix it.
> 
>> +	if ((curtime - last_pgarch_start_time) < PGARCH_RESTART_INTERVAL)
>> +		return true;
>>
>> Why did you remove the cast to unsigned int there?
> 
> The cast converts small negative values to large numbers, the code
> looks like intending to allow archiver launched when curtime goes
> behind than last_pgarch_start_time. That is the case the on-memory
> data is corrupt. I'm not sure it's worth worrying and in the first
> place if we want to care of the case we should explicitly compare the
> operands of the subtraction.  I did that in the attached.

That's an idea. But the similar calculation using that cast is used in
other places (e.g., in pgarch_MainLoop()), so I'm thinking that it's
better not to change that...


> 
> And the last_pgarch_start_time is accessed only in the function. I
> moved it to inside the function.

OK.


> 
>> +	/*
>> + * Advertise our latch that backends can use to wake us up while
>> we're
>> +	 * sleeping.
>> +	 */
>> +	PgArch->pgprocno = MyProc->pgprocno;
>>
>> The comment should be updated?
> 
> Hmm. What is advertised is our pgprocno.. Fixed.

OK.

Thanks for updating the patch! I applied some minor changes into your patch.
Attached is the updated version of the patch. I'm thinking to commit this version.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION

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.