Re: [PATCH] Lazy xid assingment V2

"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> "Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
>> Tom Lane wrote:
>>> I don't much like this, since as I mentioned before I don't think
>>> MyProc->xmin is going to be constant over a whole transaction for
>>> long. I don't think xid_age is performance-critical in any way,
>>> so I'd vote for letting it force XID assignment.
>
>> Hm... I agree that xid_age is probably not performance-critical.
>> I guess it's more the complete counter-intuitivity of forcing
>> xid assignment in some arbitrary function thats bugging me a bit.
>
> Well, I don't see it as arbitrary --- we're trying to hide the fact that
> XIDs are assigned lazily from user-visible behavior.

It seems both this and some of the other cases of having to call
ReadNewTransactionId would be eliminated if we invented a new xid treated
similarly to current_time() and others which are calculated once per
transaction and then cached for subsequent accesses. So xid_age() would
measure relative to a fixed xid, it just wouldn't be *our* xid necessarily.

Just a thought.

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com