Re: pg_try_advisory_lock is waiting?

Mladen Gogala <gogala(dot)mladen(at)gmail(dot)com> writes:
> I tried the following:

> _*1st Session:*_

> mgogala=# begin transaction;
> BEGIN
> mgogala=*# update emp set sal=sal*1 where empno=7934;
> UPDATE 1
> mgogala=*#

> _*2nd Session:*_

> mgogala=# begin transaction;
> BEGIN
> mgogala=*# select pg_try_advisory_lock(0) from (select ename from emp
> where empno=7934 for update) as tbl;

> To my infinite surprise, "pg_advisory_lock" is waiting.

I doubt it. I think the FOR UPDATE in the sub-select is blocked
because the other session has an uncommitted update on the row
it wants to lock. This command won't reach the pg_try_advisory_lock
call until that row lock comes free.

regards, tom lane