Re: old_snapshot_threshold allows heap:toast disagreement

On Sat, Jul 30, 2016 at 8:17 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Fri, Jul 29, 2016 at 1:10 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> On Wed, Jul 27, 2016 at 7:26 PM, Andres Freund <andres@anarazel.de> wrote:
>>
>> New version attached.
>
> +static inline void
> +InitToastSnapshot(Snapshot snapshot, XLogRecPtr lsn)
> +{
> + snapshot->satisfies = HeapTupleSatisfiesToast;
> + snapshot->lsn = lsn;
> +}
>
> Here, don't you need to initialize whenTaken as that is also used in
> TestForOldSnapshot_impl() to report error "snapshot too old".

Hmm, yeah.  This is actually a bit confusing.  We want the "oldest"
snapshot, but there are three different notions of "oldest":

1. Smallest LSN.
2. Smallest whenTaken.
3. Smallest xmin.

Which one do we use?

-- 
Robert Haas
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