How to diagnose application "hangs" in pg_receive?

Hi,

A hibernate based application I wrote suffers from "hangs" - the
thread which should fetch the data is stuck at pg_receive (the
function reading back data from the socket).
My first idea were threading errors, however after careful code review
I couldn't find suspicious code.
The application doesn't do any explicit locking, an excerpt of the
locking table is at the end of the email.

Any idea what could be going wrong here?
Except a broken connction, what could be the reason for never arriving
reply from the server?

Thank you in advance, Clemens

datname | relname | mode
| granted | usename | substr |
query_start | age | procpid
-------------+--------------------------------+--------------------------+---------+----------+--------------------------------+-------------------------------+-----------------+---------
khbldb_prod | startkladde_pkey | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | startkladde |
ShareUpdateExclusiveLock | t | postgres | autovacuum: VACUUM
public.star | 2011-05-21 11:19:51.780587+01 | 03:43:21.367065 |
18241
khbldb_prod | kladde_flugnr_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_schleppid_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_lehrer_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_nachplatzid_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_bmok_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_vonplatzid_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | | ExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_datum_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | statusindex | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_pilot_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | bzbisindex | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_flugzeug_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241
khbldb_prod | kladde_geschlepptid_index | RowExclusiveLock
| t | postgres | autovacuum: VACUUM public.star | 2011-05-21
11:19:51.780587+01 | 03:43:21.367065 | 18241

//No eclusive locks are held by the application:
khbldb_prod | verkauf_type_index | AccessShareLock
| t | khbl | <IDLE> in transaction | 2011-05-21
13:04:53.930505+01 | 01:58:19.217147 | 18637
khbldb_prod | rechnungsstatus_pkey | AccessShareLock
| t | khbl | <IDLE> in transaction | 2011-05-21
13:04:53.930505+01 | 01:58:19.217147 | 18637
khbldb_prod | bzbisindex | AccessShareLock
| t | khbl | <IDLE> in transaction | 2011-05-21
13:04:53.930505+01 | 01:58:19.217147 | 18637
khbldb_prod | rechnungsstatus | AccessShareLock
| t | khbl | <IDLE> in transaction | 2011-05-21
13:04:53.930505+01 | 01:58:19.217147 | 18637
khbldb_prod | kladde_lehrer_index | AccessShareLock
| t | khbl | <IDLE> in transaction | 2011-05-21
13:04:53.930505+01 | 01:58:19.217147 | 18637