Postgres LOG and NOTICE info..

Hi,

im using a jdbc connection to access postgres and somehow once i manage
transaction by myself i got some:

NOTICE: BEGIN: already a transaction in progress
NOTICE:  COMMIT: no transaction

doing :

conn = ds.getConnection();
try
{
    conn.setAutoCommit(false);
    ...
    conn.commit();
}
catch(Exception e) {conn.rollback();}
finally
{
    conn.setAutoCommit(true);
    conn.close();
}

some questions come to my mind :

Why can i have those notices since i always commit or rollback a transaction
and i left the connection in the pool in AutoCommit ? (i should ask that in
jdbc section may be)

How can i tell postgres to not log those notices ?
i have debug_level = 0 and i would like to have only true errors in my log

Thx in advance