Postgres Advisory Locks not working

Question

I am having issues with postgres advisory locks not acquiring correctly on postgres 9.4.4. If I ssh into a postgres server on two screens and open psql to acquire a lock on one and attempt to aquire the lock on another it works perfectly. However, if I do it from another server that is pointed to that server I am able to freely 'acquire' locks, but it never actually gets a lock from the database.

Normally, we use python to obtain a lock and that is where we initially noticed the issue. To obtain a lock manually I am using select pg_advisory_lock(123456789); to check which locks are out currently I am using select objid from pg_locks where locktype = 'advisory';

I will play it out here so you can visually see it and tell me what I am doing.

Attempting to get a lock using an app_server (remote server using pgbouncer) but it is failing.

app_server> psql
app_server> \c mydb
app_server> select pg_advisory_lock(123456789);
 pg_advisory_lock 
------------------

(1 row)

app_server>select objid from pg_locks where locktype = 'advisory';
 objid 
-------
(0 rows)

Using db_server to get a lock, then trying to get the lock again on app_server (remote) but on the same db.

db_server> psql
db_server> \c mydb
db_server> select pg_advisory_lock(123456789);
 pg_advisory_lock 
------------------

(1 row)

db_server> select objid from pg_locks where locktype = 'advisory';
   objid   
-----------
 123456789
(1 row)

Here you can see that db_server has the lock so I will now go back to app_server and attempt to get the same lock but this time it will work as expected where it will wait for the unlock from db_server.

app_server> select pg_advisory_lock(123456789);
...

Meanwhile, I will go unlock it from db_server.

db_server> select pg_advisory_unlock(123456789);

Immediately app_server gets and releases the lock.

servers> select objid from pg_locks where locktype = 'advisory';
 objid 
-------
(0 rows)

Answer 1

The problem is that the broken servers were using transaction based connections to postgres while the working servers were using session based connections in the pgbouncer.ini . Not sure how this was missed in our initial look at the ini.

; When server connection is released back to pool:
;   session      - after client disconnects
;   transaction  - after transaction finishes
;   statement    - after statement finishes
pool_mode = session