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

On 2016-07-19 18:09:59 -0500, Kevin Grittner wrote:
> As far as I can see, to do this the way that Andres and Amit
> suggest involves tying in to indexam.c and other code in incredibly
> ugly ways.

Could you explain the problem you're seing?

Isn't pretty much all all that we need to do:
1) add a InitSnapshotToast(Snapshot originMVCCSnap), which sets SnapshotData->lsn  to the the origin snapshot's lsn
2) adapt TestForOldSnapshot() to accept both HeapTupleSatisfiesMVCC and  HeapTupleSatisfiesToast?

I mean the only difference between toast / plain heap table WRT
old_snapshot_threshold is that we don't use a mvcc snapshot.

> I think it is entirely the wrong way to go, as I can't
> find a way to make it look remotely sane.  The question is whether
> I should do it the way that I think is sane, or whether someone
> else wants to show me what I'm missing by producing at least a
> rough patch along these lines.

I'll, but I'd prefer you explaining the problem first. Maybe it's me
missing the obvious problem.

Andres