Re: change in LOCK behavior

On 10.10.2012 22:43, Thom Brown wrote:
> On 10 October 2012 21:21, Tomas Vondra <tv@fuzzy.cz> wrote:
>> Example:
>>
>> A: BEGIN;
>> A: LOCK x IN ACCESS EXCLUSIVE MODE;
>> A: INSERT INTO x VALUES (100);
>> B: SELECT * FROM x;
>> A: COMMIT;
>>
>> Now on 9.1, B receives the value "100" while on 9.2 it gets no rows.
>>
>> Is this expected? I suspect the snapshot is read at different time or
>> something, but I've checked release notes but I haven't seen anything
>> relevant.
>>
>> Without getting the commited version of data, the locking is somehow
>> pointless for us (unless using a different lock, not the table itself).
> 
> I suspect it's this commit: d573e239f03506920938bf0be56c868d9c3416da
> 
> http://archives.postgresql.org/pgsql-committers/2011-12/msg00167.php

Maybe, the description suggests it might be related. I'm still not sure
whether this is a bug or expected behavior, although the commit clearly
states that the change shouldn't be user-visible.

Tomas