Long transaction over dblink, both sessions do nothing and waits each other.

    HelloSometimes I get very long transaction between my two databases. And see that both session do nothing.

I have two databases  USRDB and MODDB, two users USR in USRDB and MOD in MODDB

I have dblink in USR to MOD:

select * from dba_db_links where owner='USR'

OWNER DB_LINK USERNAME HOST CREATED

USR USRDB URS2MOD (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 10.61.41.30)(PORT = 1521)))(CONNECT_DATA=(SERVICE_NAME =MODDB))) 08.08.2013 05:01:27

I search long transation so

select * from v$session s, v$transaction t where t.addr=s.TADDR and s.USERNAME='URS2MOD' and t.START_date<sysdate-1

And I see that