Horton

Re: shared-memory based stats collector

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

View thread View on postgr.es
From: Fujii Masao <masao.fujii@oss.nttdata.com>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2021-03-10T06:20:43Z
Lists: pgsql-hackers 

On 2021/03/10 12:10, Kyotaro Horiguchi wrote:
> At Tue, 9 Mar 2021 23:24:10 +0900, Fujii Masao <masao.fujii@oss.nttdata.com> wrote in
>>
>>
>> On 2021/03/09 16:51, Kyotaro Horiguchi wrote:
>>> At Sat, 6 Mar 2021 00:32:07 +0900, Fujii Masao <masao.fujii@oss.nttdata.com>
>>> wrote in
>>>> I don't think that we should treat non-zero exit condition as a crash,
>>>> as before. Otherwise when archive_command fails on a signal,
>>>> archiver emits FATAL error and which leads the server restart.
>>> Sounds reasonable. Now archiver is treated the same way to wal
>>> receiver.  Specifically exit(1) doesn't cause server restart.
>>
>> Thanks!
>>
>> -			if (PgArchStartupAllowed())
>> -				PgArchPID = pgarch_start();
>>
>> In the latest patch, why did you remove the code to restart new archiver
>> in reaper()? When archiver dies, I think new archiver should be restarted like
>> the current reaper() does. Otherwise, the restart of archiver can be
>> delayed until the next cycle of ServerLoop, which may take time.
> 
> Agreed. The code moved to the original place and added the crash
> handling code. And I added a phrase to the comment.
> 
> +		 * Was it the archiver?  If exit status is zero (normal) or one (FATAL
> +		 * exit), we assume everything is all right just like normal backends
> +		 * and just try to restart a new one so that we immediately retry
>                                               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +		 * archiving of remaining files. (If fail, we'll try again in future
>             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~


"of" of "archiving of remaining" should be replaced with "the", or removed?


Just for record. Previously LogChildExit() was called and the following LOG
message was output when the archiver reported FATAL error. OTOH the patch
prevents that and the following LOG message is not output at FATAL exit of
archiver. But I don't think that the following message is required in that case
because FATAL message indicating the similar thing is already output.
Therefore, I'm ok with the patch.

LOG:  archiver process (PID 46418) exited with exit code 1


>> I read v50_003 patch.
>>
>> When archiver dies, ProcGlobal->archiverLatch should be reset to NULL,
>> like walreceiver does the similar thing in WalRcvDie()?
> 
> Differently from walwriter and checkpointer, archiver as well as
> walreceiver may die while server is running. Leaving the latch pointer
> alone may lead to nudging a wrong process that took over the same
> procarray slot. Added pgarch_die() to do that.

Thanks!

+	if (IsUnderPostmaster && ProcGlobal->archiverLatch)
+		SetLatch(ProcGlobal->archiverLatch);

The latch can be reset to NULL in pgarch_die() between the if-condition and
SetLatch(), and which would be problematic. Probably we should protect
the access to the latch by using spinlock, like we do for walreceiver's latch?


> 
> (I moved the archiverLatch to just after checkpointerLatch in this version.)
> 
>> In pgarch.c, #include "postmaster/fork_process.h" seems no longer necessary.
> 
> Right. That's not due to this patch, postmater.h, dsm.h and pg_shmem.h
> are not used. (fd.h is not necessary but pgarch.c uses AllocateDir().)
> 
>> +	if (strcmp(argv[1], "--forkarch") == 0)
>> +	{
>>
>> Why is this necessary? I was thinking that "--forkboot" handles archiver
>> in SubPostmasterMain().
> 
> Yeah, the correspondent code is removed in the same patch at the same
> time.
> 
> The attached is v51 patchset.

Thanks a lot!

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.