Robert Haas <robertmh...@gmail.com> writes: > On Tue, Dec 4, 2012 at 3:38 PM, Jeff Davis <pg...@j-davis.com> wrote: >> After reading that thread, I still don't understand why it's unsafe to >> set HEAP_XMIN_COMMITTED in those conditions. Even if it is, I would >> think that a sufficiently narrow case -- such as CTAS outside of a >> transaction block -- would be safe, along with some slightly broader >> cases (like BEGIN; CREATE TABLE; INSERT/COPY).
> I haven't looked at the committed patch - which seemed a bit > precipitous to me given the stage the discussion was at - but I > believe the general issue with HEAP_XMIN_COMMITTED is that there might > be other snapshots in the same transaction, for example from open > cursors. >From memory, the tqual.c code assumes that any tuple with XMIN_COMMITTED couldn't possibly be from its own transaction, and thus it doesn't make the tests that would be appropriate for a tuple that is from the current transaction. Maybe it's all right anyway (i.e. if we should always treat such a tuple as good) but I don't recall exactly what's tested in those paths. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers