On 12 Oct 2014, at 18:41, Arun Gokule <arun.gok...@gmail.com> wrote:

> Hi,
> 
> I am executing pg_advisory_locks using the following set of statements:
> 
>  SELECT pg_advisory_lock(317,2);
>  UPDATE posts SET dislikers = array_remove(dislikers, 7) WHERE id = 317;
>  update posts set num_dislikes = icount(dislikers), updated_at = now() where 
> id = 317;
>  WITH update_likers AS (SELECT pg_advisory_unlock(317,2)) select num_likes, 
> num_dislikes, (7 IN (select(unnest(likers)))) as liked, (7 IN 
> (select(unnest(dislikers)))) as disliked from posts where id = 317 LIMIT 1;
> 
> These are issued from a multithreaded app. One in 1000 queries, I get a 
> deadlock after the execution of the above set of statements. i.e.  SELECT 
> try_pg_advisory_lock(317,2) returns false. Is there something obvious that I 
> am doing wrong?

Your last query doesn’t call the unlock statement, that WITH section is going 
to be ignored as the query isn’t using it.

Alban Hertroys
--
If you can't see the forest for the trees,
cut the trees and you'll find there is no forest.



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