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help / color / mirror / Atom feedFrom: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Roman Eskin <r.eskin@arenadata.io>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Alexander Lakhin <exclusion@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org, Tom Lane <tgl@sss.pgh.pa.us>
Subject: Re: Avoid orphaned objects dependencies, take 3
Date: Fri, 19 Jun 2026 13:28:21 +0000
Message-ID: <ajVD9TjerBLteNlx@bdtpg> (raw)
In-Reply-To: <5591d661ea8189f5c057f6b48095f742e0d772f9.camel@j-davis.com>
References: <71eb9a8835a28165939da567a9d649fe6d21bfa7.camel@j-davis.com>
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<5591d661ea8189f5c057f6b48095f742e0d772f9.camel@j-davis.com>
Hi,
On Thu, Jun 18, 2026 at 04:21:33PM -0700, Jeff Davis wrote:
> On Wed, 2026-06-17 at 05:44 +0000, Bertrand Drouvot wrote:
> > > IIUC, this is necessary for correctness. If an ACL failure doesn't
> > > cause a transaction abort, then there's a danger that we cause the
> > > transaction to fail that should have succeeded.
> >
> > Exactly, because we'd recheck an "harmless" failed ACL check and then
> > produce
> > an error.
> >
> > > So the ACL tracking needs to be precise: we can't track an ACL
> > > check
> > > unless a failure always causes transaction abort; and we must track
> > > an
> > > ACL check if it would cause a transaction abort. Right?
> >
> > I would say: we just need to track (and recheck) ACL checks that
> > succeeded.
>
> IIUC, we cannot have false positives (tracking ACL checks that wouldn't
> have caused an abort) nor can we have false negatives (missing an ACL
> check that could cause an abort).
Right.
> It's hard for me to convince myself that we got all the cases right;
> and if we have, that they won't be broken in the future.
>
> For instance, I just realized that something else I'm working on is
> related:
>
> https://www.postgresql.org/message-id/5c629d2455946ad2fde3c184f64ea2c323ef2133.camel@j-davis.com
>
> It does an ACL check inside a subtransaction, where the parent
> transaction is a DDL statement. It happens to be a DROP statement, so
> it's not recording new dependencies, so I don't think it breaks your
> tracking mechanism, but it's too close for comfort.
I see, I don't think we have this pattern currently but yeah we may have it
in the future (and our current tracking mechanism would probably fail in such a
case).
> We could keep the transaction ID in the tracking record, and ignore
> entries from an aborted subxact. But it's getting fairly complex and
> delicate.
Agreed. We could use RegisterSubXactCallback to save/restore the entry count on
subtransaction abort, but as you say it adds complexity.
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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Subject: Re: Avoid orphaned objects dependencies, take 3
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