[EMAIL PROTECTED] (Simon Riggs) writes: > On Fri, 2008-01-11 at 20:39 +0000, Simon Riggs wrote: >> On Fri, 2008-01-11 at 15:05 -0500, Tom Lane wrote: >> Simon Riggs <[EMAIL PROTECTED]> writes: >> > > If we had a function >> > > replace_serializable_snapshot(master_xid, txid_snapshot) >> > > this would allow us to use the txid_snapshot values to replace our >> > > transaction's serializable snapshot. >> > >> > ... whereupon we'd get wrong answers. Certainly you could not allow >> > transaction xmin to go backwards, and I'm not sure what other >> > restrictions there would be, but the whole thing gives me the willies. > > Sorry, forgot to add > - global xmin isn't going backwards > - neither is latest completed xid > > The xmin of the transaction will go backwards, but as long as we don't > do anything prior to the setting of the cloned snapshot, what can go > wrong? :-)
Note that we required that the "provider transaction" have the attributes IsXactIsoLevelSerializable and XactReadOnly both being true, so we have the mandates that the resultant backend process: a) Is in read only mode, and b) Is in serializable mode. That's a pair of (possibly stretching-wide!) suspenders worth of support from Evil... -- (format nil "[EMAIL PROTECTED]" "cbbrowne" "cbbrowne.com") http://linuxfinances.info/info/internet.html Trying to be happy is like trying to build a machine for which the only specification is that it should run noiselessly. ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
