Re: getting rid of SnapshotNow

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Fri, Jul 26, 2013 at 9:18 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>> Well, that's still used in _bt_check_unique, unique_key_recheck
>>> (trigger function to do a deferred uniqueness check), RI_FKey_check,
>>> and rather extensively by sepgsql. I don't really have much desire to
>>> do the work to get rid of it, though.

>> Hm. I agree the first three may be all right, but I can't help
>> suspecting that sepgsql is doing the wrong thing here.

> sepgsql is using SnapshotSelf to find the old version of a tuple that
> was updated by the core code just before.

Oh. OK, then it reduces to the same case as the other three, ie we're
looking at tuples we know to be update-locked.

> [ interesting ruminations snipped ]

Yeah, removing SnapshotNow catalog access certainly opens the doors
for a lot of new thinking.

regards, tom lane