Horton

Re: shared-memory based stats collector

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Cc: tomas.vondra@2ndquadrant.com, alvherre@2ndquadrant.com, ah@cybertec.at, magnus@hagander.net, robertmhaas@gmail.com, tgl@sss.pgh.pa.us, pgsql-hackers@postgresql.org
Date: 2019-02-15T17:16:55Z
Lists: pgsql-hackers 
Hi,

On 2019-02-15 17:29:00 +0900, Kyotaro HORIGUCHI wrote:
> At Thu, 7 Feb 2019 13:10:08 -0800, Andres Freund <andres@anarazel.de> wrote in <20190207211008.nc3axviivmcoaluq@alap3.anarazel.de>
> > Hi,
> > 
> > On 2018-11-12 20:10:42 +0900, Kyotaro HORIGUCHI wrote:
> > > diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
> > > index 7eed5866d2..e52ae54821 100644
> > > --- a/src/backend/access/transam/xlog.c
> > > +++ b/src/backend/access/transam/xlog.c
> > > @@ -8587,9 +8587,9 @@ LogCheckpointEnd(bool restartpoint)
> > >  						&sync_secs, &sync_usecs);
> > >  
> > >  	/* Accumulate checkpoint timing summary data, in milliseconds. */
> > > -	BgWriterStats.m_checkpoint_write_time +=
> > > +	BgWriterStats.checkpoint_write_time +=
> > >  		write_secs * 1000 + write_usecs / 1000;
> > > -	BgWriterStats.m_checkpoint_sync_time +=
> > > +	BgWriterStats.checkpoint_sync_time +=
> > >  		sync_secs * 1000 + sync_usecs / 1000;
> > 
> > Why does this patch do renames like this in the same entry as actual
> > functional changes?
> 
> Just because it is no longer "messages". I'm ok to preserve them
> as historcal names. Reverted.

It's fine to do such renames, just do them as separate patches. It's
hard enough to review changes this big...


> > >  /*
> > >   * Structures in which backends store per-table info that's waiting to be
> > > @@ -189,18 +189,14 @@ typedef struct TabStatHashEntry
> > >   * Hash table for O(1) t_id -> tsa_entry lookup
> > >   */
> > >  static HTAB *pgStatTabHash = NULL;
> > > +static HTAB *pgStatPendingTabHash = NULL;
> > >  
> > >  /*
> > >   * Backends store per-function info that's waiting to be sent to the collector
> > >   * in this hash table (indexed by function OID).
> > >   */
> > >  static HTAB *pgStatFunctions = NULL;
> > > -
> > > -/*
> > > - * Indicates if backend has some function stats that it hasn't yet
> > > - * sent to the collector.
> > > - */
> > > -static bool have_function_stats = false;
> > > +static HTAB *pgStatPendingFunctions = NULL;
> > 
> > So this patch leaves us with a pgStatFunctions that has a comment
> > explaining it's about "waiting to be sent" stats, and then additionally
> > a pgStatPendingFunctions?
> 
> Mmm. Thanks . I changed the comment and separated pgSTatPending*
> stuff from there and merged with pgstat_pending_*. And unified
> the naming.

I think my point is larger than that - I don't see why the pending
hashtables are needed at all. They seem purely superflous.


> > 
> > > +	if (cxt->tabhash)
> > > +		dshash_detach(cxt->tabhash);
> > 
> > Huh, why do we detach here?
> 
> To release the lock on cxt->dbentry. It may be destroyed.

Uh, how?



> - Separte shared database stats from db_stats hash.
> 
> - Consider relaxing dbentry locking.
> 
> - Try removing pgStatPendingFunctions
> 
> - ispell on it.

Additionally:
- consider getting rid of all the pending stuff, not just for functions,
  - as far as I can tell it's unnecessary

Thanks,

Andres

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.