PostgreSQL Advisory Locking

AdvisoryLocking.sql

<tableid> = select oid from pg_class where relname = '<tablename>';
<rowid> = select id from (
    select rr.id from <tablename> rr left join pg_locks pgl
    on pgl.classid = <tableid> and pgl.objid = rr.id
    where pgl.objid is null limit 1
) iq where pg_try_advisory_lock(<tableid>, id);

-- select * from pg_locks where locktype = 'advisory';

select pg_advisory_unlock(<tableid>, <rowid>);

http://www.postgresql.org/docs/9.1/interactive/functions-admin.html

select pg_try_advisory_lock(<tableid>, id) from <tablename> where id = <rowid>;