Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <

On Thu, Jun 16, 2016 at 12:54 PM, Andres Freund <andres@anarazel.de> wrote:
>> The root of my confusion is: if we prune a tuple, we'll bump the page
>> LSN, so any session that is still referencing that tuple will error
>> out as soon as it touches the page on which that tuple used to exist.
>
> Right. On the main table. But we don't peform that check on the toast
> table/pages. So if we prune toast tuples, which are still referenced by
> (unvacuumed) main relation, we can get into trouble.

OK, if it's true that we don't perform that check on the TOAST table,
then I agree there's a potential problem there.  I don't immediately
know where in the code to look to check that.

--
Robert Haas
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