Re: Re-read conindid under the referenced table's lock in the RI fast path

On Mon, Aug 31, 2026 at 10:53 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> On Tue, Aug 18, 2026 at 5:34 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> > On Mon, Aug 17, 2026 at 10:17 PM Mihail Nikalayeu
> > <mihailnikalayeu(at)gmail(dot)com> wrote:
> > > On Mon, Aug 17, 2026 at 3:07 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> > > > Thanks. Attached is v2 of the patch posted here. I adjusted the commit
> > > > message and comments, kept you credited as Author, and replaced the
> > > > Opus co-author trailer with a disclosure sentence, which I can remove
> > > > if you so prefer.
> > >
> > > I'm not sure it's required, I think using some AI tool is the new
> > > default now, at least for some phases.
> >
> > Ok, removed.
> >
> > > > I will push this tomorrow.
> >
> > Done.
>
> While testing the fastpath code with the batching layer reverted, I
> hit a case where ri_FastPathCheck() , the per-row path taken when a
> batch isn't in play, rejects a valid row. It registers the snapshot
> for its index scan before table_open() on the referenced relation, so
> anything committed while it waits for that lock is invisible. If the
> referenced row commits, the check reports a violation for a key that
> exists.
>
> The fastpath is meant to be semantically equivalent to the SPI path,
> so I checked what that does here. RI_FKey_check() passes
> detectNewRows = false, so ri_PerformCheck() passes InvalidSnapshot
> rather than an explicit snapshot. _SPI_execute_plan() then calls
> GetCachedPlan(), which locks the relations, before it reaches
> PushActiveSnapshot(GetTransactionSnapshot()). ri_FastPathCheck() does
> its own opening and scanning, so there is no plan cache to force that
> ordering; the snapshot is acquired directly, and it was placed before
> the table_open() rather than after.
>
> Patch attached, moving the acquisition after table_open() and the
> constraint re-read.
>
> Will add an open item once this hits the archive.

Done:

Stale snapshot in RI fast-path leads to spurious failure
Commit: 2da86c1ef9b
Owner: Amit Langote

--
Thanks, Amit Langote