Re: pg advisory locks

[Arun Gokule <arun.gokule@xxxxxxxxx>]

Also I noticed that executing the following query:

  SELECT *

FROM

(

    SELECT DISTINCT age(now(), query_start) AS age, pg_stat_activity.pid,pg_locks.granted,pg_stat_activity.application_name,pg_stat_activity.backend_start, pg_stat_activity.xact_start, pg_stat_activity.state_change, pg_stat_activity.waiting, pg_stat_activity.state, pg_stat_activity.query_start, left(pg_stat_activity.query, 60)

    FROM pg_stat_activity, pg_locks

    WHERE pg_locks.pid = pg_stat_activity.pid

) AS foo

WHERE age > '30 seconds'

ORDER BY age DESC;

I get 2 entries for the pid 78573 with one as granted = true and the other as granted =false but they have the same timestamps. See below:

       age       |  pid  | granted | application_name |         backend_start         |          xact_start           |         state_change          | waiting | state  |          query_start          |                             left

-----------------+-------+---------+------------------+-------------------------------+-------------------------------+-------------------------------+---------+--------+-------------------------------+--------------------------------------------------------------

 10:53:25.394862 | 78261 | t       | bin/rails        | 2014-10-12 05:20:04.543242-07 |                               | 2014-10-12 08:57:22.950505-07 | f       | idle   | 2014-10-12 08:57:22.949693-07 | SELECT pg_advisory_lock(317,2);UPDATE posts SET dislikers =

 10:53:23.50218  | 78573 | t       | bin/rails        | 2014-10-12 05:37:58.120879-07 | 2014-10-12 08:57:24.842375-07 | 2014-10-12 08:57:24.842379-07 | t       | active | 2014-10-12 08:57:24.842375-07 | SELECT pg_advisory_lock(317,2);UPDATE posts SET likers = arr

 10:53:23.50218  | 78573 | f       | bin/rails        | 2014-10-12 05:37:58.120879-07 | 2014-10-12 08:57:24.842375-07 | 2014-10-12 08:57:24.842379-07 | t       | active | 2014-10-12 08:57:24.842375-07 | SELECT pg_advisory_lock(317,2);UPDATE posts SET likers = arr

 00:57:53.495221 | 90360 | t       | bin/rails        | 2014-10-12 18:43:20.09202-07  |                               | 2014-10-12 18:52:54.849397-07 | f       | idle   | 2014-10-12 18:52:54.849334-07 | SELECT "posts"."id" AS t0_r0, "posts"."content" AS t0_r1, "p

On Sun, Oct 12, 2014 at 9:41 AM, Arun Gokule <arun.gokule@xxxxxxxxx> 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?

Thanks,

Arun

--

Thanks,

Arun