Robert Haas <robertmhaas@gmail.com> writes:
> On Jul 2, 2012, at 12:04 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> On Jul 1, 2012, at 4:18 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> However, I'm a bit worried by the "if (!FirstSnapshotSet)" restriction
>>> in GetLatestSnapshot.
>> I don't know whether it should set the transaction snapshot or just r
> Argh, sorry.
> ...or just return a current snapshot, and I also don't know whether it needs to be changed because of this; but I
agreewith changing it. Erroring out always seemed kind of pointless to me...
I think it was coded like that because the sole original use was in
ri_triggers.c, in which it would have been a red flag if no transaction
snapshot already existed. However, the restriction clearly doesn't fit
with GetLatestSnapshot's API spec, so it seems to me to be sensible
to change it (as opposed to, say, inventing a new snapshot function
with a subtly different API spec).
As for creating an MVCC snapshot without causing a transaction snapshot
to be established, no thanks --- that would create a path of control
that exists nowhere today and has gotten no testing at all. I suspect
that it might actively break some assumptions in snapshot management.
regards, tom lane