Horton

Re: shared-memory based stats collector - v70

Drouvot, Bertrand <bdrouvot@amazon.com>

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From: "Drouvot, Bertrand" <bdrouvot@amazon.com>
To: Andres Freund <andres@anarazel.de>, Greg Stark <stark@mit.edu>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Melanie Plageman <melanieplageman@gmail.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Thomas Munro <thomas.munro@gmail.com>, "David G. Johnston" <david.g.johnston@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-08-19T06:12:51Z
Lists: pgsql-hackers 
Hi,

On 8/18/22 9:51 PM, Andres Freund wrote:
> Hi,
>
> On 2022-08-18 15:26:31 -0400, Greg Stark wrote:
>> And indexes of course. It's a bit frustrating since without the
>> catalog you won't know what table the index actually is for... But
>> they're pretty important stats.
> FWIW, I think we should split relation stats into table and index
> stats. Historically it'd have added a lot of complexity to separate the two,
> but I don't think that's the case anymore. And we waste space for index stats
> by having lots of table specific fields.

It seems to me that we should work on that first then, what do you 
think? (If so I can try to have a look at it).

And once done then resume the work to provide the APIs to get all 
tables/indexes from all the databases.

That way we'll be able to provide one API for the tables and one for the 
indexes (instead of one API for both like my current POC is doing).

>> On that note though... What do you think about having the capability
>> to add other stats kinds to the stats infrastructure?

I think that's a good idea and that would be great to have.

> Getting closer to that was one of my goals working on the shared memory stats
> stuff.
>
>
>> It would make a lot of sense for pg_stat_statements to add its entries here
>> instead of having to reimplement a lot of the same magic.
> Yes, we should move pg_stat_statements over.
>
> It's pretty easy to get massive contention on stats entries with
> pg_stat_statements, because it doesn't have support for "batching" updates to
> shared stats. And reimplementing the same logic in pg_stat_statements.c
> doesn't make sense.
>
> And the set of normalized queries could probably stored in DSA as well - the
> file based thing we have right now is problematic.
>
>
>> To do that I guess more of the code needs to be moved to be table
>> driven from the kind structs either with callbacks or with other meta
>> data.
> Pretty much all of it already is. The only substantial missing bit is
> reading/writing of stats files, but that should be pretty easy. And of course
> making the callback array extensible.
>
>
>> So the kind record could contain tupledesc and the code to construct the
>> returned tuple so that these functions could return any custom entry as well
>> as the standard entries.
> I don't see how this would work well - we don't have functions returning
> variable kinds of tuples. And what would convert a struct to a tuple?
>
> Nor do I think it's needed - if you have an extension providing a new stats
> kind it can also provide accessors.

I think the same (the extension should be able to do that).

I really like the idea of being able to provide new stats kind.

Regards,

-- 
Bertrand Drouvot
Amazon Web Services: https://aws.amazon.com

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.