On the magic web I found this script at Jared Still’s blog. It allows to see which database links are being used and by whom. Information sometimes useful (needs to be run as SYSDBA):
-- who is querying via dblink?
-- Courtesy of Tom Kyte, via Mark Bobak
-- this script can be used at both ends of the database link
-- to match up which session on the remote database started
-- the local transaction
-- the GTXID will match for those sessions
-- just run the script on both databases
Select /*+ ORDERED */
substr(s.ksusemnm,1,10)||'-'|| substr(s.ksusepid,1,10) "ORIGIN",
substr(g.K2GTITID_ORA,1,35) "GTXID",
substr(s.indx,1,4)||'.'|| substr(s.ksuseser,1,5) "LSESSION" ,
s2.username,
substr(
decode(bitand(ksuseidl,11),
1,'ACTIVE',
0, decode( bitand(ksuseflg,4096) , 0,'INACTIVE','CACHED'),
2,'SNIPED',
3,'SNIPED',
'KILLED'
),1,1
) "S",
substr(w.event,1,10) "WAITING"
from x$k2gte g, x$ktcxb t, x$ksuse s, v$session_wait w, v$session s2
where g.K2GTDXCB =t.ktcxbxba
and g.K2GTDSES=t.ktcxbses
and s.addr=g.K2GTDSES
and w.sid=s.indx
and s2.sid = w.sid