Horton

Re: BUG #19520: PANIC when concurrently manipulating stored procedures with pg_stat_statements and track_functions =

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Sami Imseih <samimseih@gmail.com>
Cc: Ayush Tiwari <ayushtiwari.slg01@gmail.com>, zlh21343@163.com, pgsql-bugs@lists.postgresql.org, Andres Freund <andres@anarazel.de>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Date: 2026-06-18T01:03:40Z
Lists: pgsql-bugs

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On Wed, Jun 17, 2026 at 03:26:33PM -0500, Sami Imseih wrote:
>> Was the idea to leave it as a backstop, or would folding the handling into
>> one place (or making _internal's an Assert) be cleaner?
> 
> The check in _internal should be converted to an Assert. This documents
> that callers  must only pass "live" entries, which will be the case
> for all callers after
> the patch

Yeah, I was hesitating to do so, but perhaps you are right that there
is little meaning in keeping this extra elog() anymore in the internal
routine: all its callers discard entries marked as dropped.  And we do
so while holding an exclusive lock.

>> - In the missing_ok path the wrapper returns true, so the post-commit
>>   caller skips the not_freed_count++/GC request that a "real" not-freed
>>   drop would do.  That seems harmless since the entry self-heals
>>   but was returning true there a deliberate choice over mirroring
>>   the not-freed/false path? I need to take a look again at this, maybe
>>   I missed something.
> 
> Finding an already dropped entry tells me that the first caller to drop the
> entry also triggered a gc request, so we should not request it again.

Nope, we should not trigger multiple requests.

Attaching an updated patch for now.  I am still testing it locally
across all the branches to make sure that the issue is gone (that
takes quite a bit of time).  I'll probably apply it in a few hours
down to v15 if nothing pops up.
--
Michael

Commits

  1. Re-introduce pgstat_drop_entry(), keeping ABI compatibility

  2. Update .abi-compliance-history for pgstat_drop_entry()

  3. Fix PANIC with track_functions due to concurrent drop of pgstats entries