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Re: Adding locks statistics

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Tomas Vondra <tomas@vondra.me>, Andres Freund <andres@anarazel.de>, Jeff Davis <pgsql@j-davis.com>, Greg Sabino Mullane <htamfids@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2026-04-06T05:11:21Z
Lists: pgsql-hackers 
On Tue, Mar 31, 2026 at 07:10:51AM +0000, Bertrand Drouvot wrote:
> On Mon, Mar 30, 2026 at 06:11:17PM +0200, Tomas Vondra wrote:
>> Isn't pgstat_lock_flush_cb a bit broken with nowait=true? It'll skip
>> flushing stats for that particular lock type, but then it'll happily
>> reset the pending stats anyway, forgetting the stats.
>> 
>> AFAIK it should keep the pending stats, and flush them sometime lager,
>> when the lock is not contended. That's what the other flush callbacks
>> do, at least. This probably means it needs to reset the entries one by
>> one, not the whole struct at once.
> 
> Oh right, it's currently misbehaving, thanks for the warning!

Not misbehaving, mistaken.  This would create loss of stats data that
should have been flushed.  I should not have missed that, sorry about
that.  A single-lock approach is also something we do for SLRU and WAL
data, and these are much hotter.

At the exception of one comment that could be simplified, the code
removed is correct, so addressed this one as well. 
--
Michael

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix injection point detach timing problem in TAP test for lock stats

  2. Use single LWLock for lock statistics in pgstats

  3. Add tests for lock statistics, take two

  4. Remove isolation test lock-stats

  5. Avoid including clog.h in proc.h

  6. Don't include storage/lock.h in so many headers

  7. Add support for lock statistics in pgstats

  8. Move some code blocks in lock.c and proc.c

  9. Move declarations related to locktags from lock.h to new locktag.h