Hannu Krosing <[EMAIL PROTECTED]> writes:
> Tom Lane wrote:
>> I do not believe it is safe to drop read locks intra-transaction, and
>> I am unwilling to take a chance on it being safe so close to 7.1 beta.
> Will we still have readers-dont-block-writers behaviour?
Sure. The only thing this really affects is VACUUM and schema-altering
commands, which will now have to wait until reader transactions commit.
In other words
Session 1 Session 2
BEGIN;
SELECT * FROM foo;
ALTER TABLE foo ...
...
COMMIT;
Session 2 will have to wait for session 1 to commit; before it didn't.
An example of why this is a good idea is
Session 1 Session 2
BEGIN;
DECLARE c CURSOR FOR
SELECT * FROM foo;
ALTER TABLE foo ...
FETCH FROM c;
COMMIT;
Without a held read lock on foo, session 1 is in deep trouble,
because its cursor is no longer correctly planned.
regards, tom lane
