On Sun, Mar 04, 2012 at 01:02:57PM +0000, Simon Riggs wrote: > More detailed thoughts show that the test in heap_beginscan_internal() > is not right enough, i.e. wrong. > > We need a specific XidInMVCCSnapshot test on the relvalidxid, so it > needs to be a specific xid, not an xmin because otherwise we can get > concurrent transactions failing, not just older transactions.
Good point; I agree. indcheckxmin's level of pessimism isn't appropriate for this new check. > If we're going freeze tuples on load this needs to be watertight, so > some minor rework needed. > > Of course, if we only have a valid xid on the class we might get new > columns added when we do repeated SELECT * statements using the same > snapshot while concurrent DDL occurs. That is impractical, so if we > define this as applying to rows it can work; if we want it to apply to > everything its getting more difficult. Excess columns seem less grave to me than excess or missing rows. I'm having difficulty thinking up an explanation for that opinion. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
