Re: BUG #4125: Strange ALTER TABLE behavior

"Vladimir Kanazir" <vladimir@vlajko.com> writes:
> If I execute this query:
> alter table history add incoming_id bigint default 0;

> the table will be locked until operation finishes (checked by executing the
> select query on the same table via another connection).

Indeed, because it has to physically fill the value zero into every
table row.

> But, if I do this:
> alter table history add incoming_id bigint;
> alter table history alter incoming_id set default 0;
> update history set incoming_id=0;
> the table will be locked only during alter table execution, which is very
> short time.

But this exposes the state where incoming_id isn't zero to other
transactions.

            regards, tom lane