On Sun, Aug 23, 2009 at 7:00 PM, Tom Lane<tgl@xxxxxxxxxxxxx> wrote: > Greg Stark <gsstark@xxxxxxx> writes: >> The last tuple is marked strangely I think. I don't think it's >> supposed to have XMAX_INVALID if xmax is 0 but I could be wrong. Also, >> I don't understand why it's marked as UPDATED if ctid and xmax aren't >> set. > > No, that all looks right to me. UPDATE sets HEAP_UPDATED on the newer > version of the row, not the older one. What looks interesting to me is > that the last update isn't marked HEAP_ONLY_TUPLE, ie, it's not in the > same HOT chain. Why is that I wonder ... > >> I'm wondering if the page allvisible flag is set. The visibility map >> is one of the few 8.4 patches which impact transaction visibility. > > But we don't use that while examining individual tuples, do we? We don't use the visibility map itself but we *do* use the page header's all visible bit. On a sequential scan we skip the visibility check for tuples on the page if the page header bit is set. -- greg http://mit.edu/~gsstark/resume.pdf -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
