Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > Kevin Grittner <kgrittn@xxxxxxxxx> writes: >> Why don't we rewrite tuples with their existing xid in such >> cases? The current state of affairs seem to me to be a pretty >> clear bug. > > No, it isn't --- the tuple is being modified by the ALTER > command. If a REPEATABLE READ or SERIALIZABLE transaction cannot see the state of a table as of the point it took its snapshot, that is a bug. There are reasonable arguments why the right fix isn't to keep the same xmin value, but that doesn't make the current situation less of a bug. A REPEATABLE READ or SERIALIZABLE transaction can currently see a table as completely empty, even if it was not in that state at any point since the transaction began. Heck, it can be seen in that state even if it was *never* visible in that state -- for example, it was created with rows by SELECT INTO and has never had all rows deleted or truncated since. If an UPDATE modified the tuples you could never see things in such an inconsistent state. -- Kevin Grittner EDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
