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Re: Avoid orphaned objects dependencies, take 3

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Robert Haas <robertmhaas@gmail.com>, Roman Eskin <r.eskin@arenadata.io>, Michael Paquier <michael@paquier.xyz>, Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers@lists.postgresql.org, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2026-06-03T18:08:13Z
Lists: pgsql-hackers 
On Mon, 2026-06-01 at 09:21 +0000, Bertrand Drouvot wrote:
> Now that we avoid orphaned objects dependencies, I resumed working on
> Robert's
> concern about the TOCTOU window where a REVOKE could land between the
> original
> permission check and the dependency recording.
> 
> Based on our discussion during PGConf.dev, PFA a new patch that uses
> the same
> approach as RangeVarGetRelidExtended(): record
> SharedInvalidMessageCounter at the
> time of the original aclcheck, then before locking compare the
> current counter to
> the saved value. If it changed, recheck permission before acquiring
> the lock.
> After the lock wait, if more invalidations arrived, release and
> retry.

RangeVarGetRelidExtended() coordinates three things:

  - name lookup
  - lock
  - ACL check

whereas recheckAclAndLock() only coordinates the latter two. That means
there can still be some strange failures, like:

  -- Session 1
  BEGIN;
  DROP SCHEMA s2;

  -- Session 2
  SET search_path=s2, s1;
  CREATE FUNCTION f() RETURNS INT LANGUAGE plpgsql AS
    $$ BEGIN RETURN 42; END; $$;

  -- Session 1
  COMMIT;

  -- Session 2
  ERROR:  referenced schema was concurrently dropped

even though no schema was actually referenced in the query, and a retry
of the transaction successfully creates the function in s1. Is that
expected?

Regards,
	Jeff Davis

Commits

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

  1. Avoid orphaned objects dependencies

  2. Don't try to record dependency on a dropped column's datatype