Re: XID wraparound and busy databases

>>> On Wed, Aug 15, 2007 at  5:06 PM, in message <7968.1187215570@sss.pgh.pa.us>,
Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Treat <xzilla@users.sourceforge.net> writes:
>> I'm a little confused, wouldnt the transaction that waits 30 minutes before
>> modifying data need to get an XID that jives with the system when it's
>> transaction started, not when it began manipulating data?
>
> Why?
>
>> Would it really be safe to take a new snapshot at that time,
>
> You wouldn't take a new snapshot.  The thought that occurs to me is that
> there's no reason that a transaction has to have an XID for itself
> before it takes a snapshot.  We always special-case our own XID anyway.

I'm having trouble picturing how that would work with a transaction using
the SERIALIZABLE transaction isolation level, or would this just be done at
the READ COMMITTED level?

-Kevin