Re: Weird locking situation

Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au> writes:
> What is going on here? Surely getting a FOR UPDATE row lock should
> prevent another process getting an update lock?

I could not duplicate your results. I did

regression=# create table tab(id int , blah int);
CREATE TABLE
regression=# insert into tab values(1,1);
INSERT 320558 1
regression=# insert into tab values(1,2);
INSERT 320559 1
regression=# insert into tab values(2,3);
INSERT 320560 1
regression=# BEGIN;
BEGIN
regression=# SELECT * FROM tab WHERE id=1 FOR UPDATE;
id | blah
----+------
1 | 1
1 | 2
(2 rows)

<< in another window >>

regression=# UPDATE tab SET blah=1 WHERE id=1;
[waits]

<< back to first window >>

regression=# UPDATE tab SET blah=1 WHERE id=1;
UPDATE 2
regression=# end;
COMMIT

<< second window now reports >>

UPDATE 2
regression=#

The behavior you describe would certainly be a bug, but you'll have to
show a reproducible example to convince me it wasn't pilot error. One
idea that springs to mind is that maybe additional rows with id=1 were
inserted (by some other transaction) between the SELECT FOR UPDATE and
the UPDATE?

regards, tom lane