On Wed, Jan 5, 2011 at 3:00 PM, Simon Riggs <si...@2ndquadrant.com> wrote: > On Mon, 2011-01-03 at 23:13 -0500, Robert Haas wrote: > >> > Hmmm, my earlier code took xmax only if xmax > xmin. That was wrong; >> > what I have now is better, but your point is there may be an even better >> > truth. I'll think on that a little more. > > I remember that I thought some more on this and decided that I couldn't > see a problem. I also see I didn't update the list to say that. > >> I guess the problem case here is something like: >> >> 1. T1 begins. T1 writes a tuple A (so it gets an XID). >> 2. T2 begins. T2 writes a tuple B (so it gets a later XID). >> 3. T1 takes a new snapshot that can see B and deletes B. >> 4. T2 commits. >> 5. T1 commits. > > How is step (3) possible before step (4)?
At read committed isolation level, which is the default, we take a new snapshot after every command. > There are later errors in your example also. Well, point them out and let's discuss. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
