DB Version:11.2.0.4
Platform : RHEL 6.5
Below is the output from a 4-node RAC DB. So, is it safe to assume that V$SESSION.SID will unique for an Instance , but you can have multiple sessions with the same serial# ?
--- No duplicate SIDs in an Instance
SQL> select inst_id, sid, count(*) from gv$session group by inst_id, sid
having count(*) > 1
order by count(*) desc ; 2 3
no rows selected
---- Duplicate SERIAL#s exist in an Instance
SQL> select inst_id, serial#, count(*) from gv$session group by inst_id, serial#
having count(*) > 1
order by count(*) desc 2 3 ;
INST_ID SERIAL# COUNT(*)
---------- ---------- ----------
2 1 56
1 1 56
4 1 55
3 1 54
4 3 5
3 3 4
2 3 4
1 3 3
2 28727 2
4 34285 2
4 10679 2
4 28787 2
2 17549 2
1 57249 2
2 623 2
4 56203 2
1 10859 2
2 6147 2
2 2135 2
4 57565 2
1 65041 2
2 19889 2
1 34633 2
23 rows selected.