Re: Avoiding pin scan during btree vacuum

Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> I think the new comment that talks about Toast Index should explain
> *why* we can skip the pinning in all cases except that one, instead of
> just saying we can do it.

I've not looked at that code in a long while, but my recollection is
that it's designed that way to protect non-MVCC catalog scans, which
are gone now ... except for SnapshotToast. 

Maybe the right way to
approach this is to adjust HeapTupleSatisfiesToast (or maybe just
convince ourselves that no one could be dereferencing a stale toast
pointer in the first place?) and then redesign btree vacuuming without
the requirement to support non-MVCC scans, period.