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>, andres@anarazel.de
Cc: gkokolatos@protonmail.com, pgsql-hackers@lists.postgresql.org
Date: 2021-03-11T06:33:52Z
Lists: pgsql-hackers 

On 2021/03/11 13:42, Kyotaro Horiguchi wrote:
> At Wed, 10 Mar 2021 19:21:00 -0800, Andres Freund <andres@anarazel.de> wrote in
>> Hi,
>>
>> Two minor nits:
> 
> Thanks for the comments!
> 
>> On 2021-03-10 21:47:51 +0900, Fujii Masao wrote:
>>> +/* Shared memory area for archiver process */
>>> +typedef struct PgArchData
>>> +{
>>> +	Latch	   *latch;			/* latch to wake the archiver up */
>>> +	slock_t		mutex;			/* locks this struct */
>>> +} PgArchData;
>>> +
>>
>> It doesn't really matter, but it'd be pretty trivial to avoid needing a
>> spinlock for this kind of thing. Just store the pgprocno of the archiver
>> in PgArchData.
> 
> Looks promising.

You mean that spinlock is not necessary by doing the followings?

- Save pgprocno of archiver in PgArchData, instead of latch and mutex.
- Set PgArch->pgprocno at the startup of archiver
- Reset PgArch->pgprocno to INVALID_PGPROCNO at pgarch_die()
- XLogArchiveNotify() sets the latch (i.e., &ProcGlobal->allProcs[PgArch->pgprocno].procLatch) if PgArch->pgprocno is not INVALID_PGPROCNO

Right?


> 
>> While getting rid of the spinlock doesn't seem like a huge win, it does
>> seem nicer that we'd automatically have a way to find data about the
>> archiver (e.g. pid).
> 
> PGPROC GetAuxProcessInfo(AuxProcType type)?

I don't think this new function is necessary.

ISTM that Andres said that it's worth adding pgprocno into PgArch because
which enables us to get the information about archiver more easily by
using that pgprocno. For example, we can get the pid of archiver by
&ProcGlobal->allProcs[PgArch->pgprocno].pid. That is, he thinks that
adding pgprocno has several merits. I agree that. Maybe I'm misunderstanding
his comment, though...


> 
>>> 		 * checkpointer to exit as well, otherwise not. The archiver, stats,
>>> 		 * and syslogger processes are disregarded since they are not
>>> 		 * connected to shared memory; we also disregard dead_end children
>>> 		 * here. Walsenders are also disregarded, they will be terminated
>>> 		 * later after writing the checkpoint record, like the archiver
>>> 		 * process.
>>> 		 */
>>
>> This comment in PostmasterStateMachine() is outdated now.
> 
> Right. Will fix a bit later.

Thanks!

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.