duncan.burke@orionvm.com.au writes:
> I found that running a SELECT FOR UPDATE query in a CTE does not block
> simultaneous transactions from running the same query.
The reason this test case doesn't do anything:
> CREATE FUNCTION lock_0(int) returns int as $$
> WITH locked as (
> SELECT 1 FROM foo
> WHERE x = $1
> FOR UPDATE)
> SELECT 1
> $$ LANGUAGE SQL;
is that the CTE is unreferenced. While we force INSERT/UPDATE/DELETE
CTEs to be executed even when not referenced, that does not apply to
SELECTs; see
http://www.postgresql.org/docs/9.1/static/queries-with.html
which states "execution of a SELECT is carried only as far as the
primary query demands its output".
If I change the function to say "WITH ... SELECT * FROM locked" then
blocking occurs as expected.
regards, tom lane