Re: ACCESS EXCLUSIVE lock

On Wed, 2006-10-18 at 09:24, Atesz wrote:
> Hi!
>
> I have a problem with ACCESS EXCLUSIVE lock when I drop a reference in
> transaction. I have 2 tables:
> create table a(id SERIAL primary key);
> create table b(id SERIAL primary key references a(id));
>
> After that I have 2 processes: P1, P2
> In P1:
> begin;
> ALTER TABLE b DROP CONSTRAINT b_id_fkey;
>
> In P2:
> SELECT * FROM a;
>
> And I'm waiting for the result, but I don't get until P1 finishes.
> I know the DROP CONSTRAINT put an ACCESS EXCLUSIVE table LOCK into the
> TABLE a, and the SELECT is stopped by this LOCK in P2.
> Note: I cannot commit the P1 earlier, because it's a very long
> transaction (more hours, data conversion transaction)
> My question: Why need this strict locking?
>
> In my opinion there isn't exclusion between the DROP CONSTRAINT and the
> SELECT.

What if, a minute or two after the drop contraint, you issue a rollback?