YOu can check this with the following query... i.e. the number of records in a rows in a transaction in the rollback.

SELECT SUBSTR(a.os_user_name,1,8) "OS User"
, SUBSTR(a.oracle_username,1,16) "DB User"
, SUBSTR(b.owner,1,16) "Schema"
, SUBSTR(b.object_name,1,25) "Object Name"
, SUBSTR(b.object_type,1,10) "Type"
, SUBSTR(c.segment_name,1,11) "RBS"
, SUBSTR(d.used_urec,1,12) "# of Records"
FROM v$locked_object a
, dba_objects b
, dba_rollback_segs c
, v$transaction d
, v$session e
WHERE a.object_id = b.object_id
AND a.xidusn = c.segment_id
AND a.xidusn = d.xidusn
AND a.xidslot = d.xidslot
AND d.addr = e.taddr
;