px-slaves and gv$session

While troubleshooting some problem on a RAC database for a customer, I queried gv$session. I knew I was the only user logged in with my username, but somehow I found four rows in gv$session for my one session. Some further investigation told me this:

MY_USER@SOME_DB SQL> select inst_id, username
  2    from gv$session
  3   where username = ‘MY_USER’;

   INST_ID USERNAME
———- ——————–
         1 MY_USER
         1 MY_USER
         2 MY_USER
         3 MY_USER

Obviously I was annoyed by the fact that four results came back from gv$session, even though I was the only person logged in. Luckily my colleague Jeroen explained to me that I was completely overlooking the fact that querying gv$session actually invokes a parallel query over the complete RAC:

MY_USER@SOME_DB SQL> select inst_id, osuser, program
2 from gv$session
3 where username = ‘MY_USER’;

INST_ID OSUSER PROGRAM
———- ——————– ————————————————–
1 LandlustJH sqlplus@some_server.nl (TNS V1-V3)
1 LandlustJH oracle@some_server.nl (PZ99)
2 LandlustJH oracle@some_server.nl (PZ99)
3 LandlustJH oracle@some_server.nl (PZ99)

Somehow I could have know this…. Somehow this also might explain why sometimes EM gives four audit alerts after one login. Anyway, this post is to share this with the world: remember that sometimes results from Oracle seem wrong, but in fact they’re not.

P.S.: and call Jeroen if you need a real pro on the job 😉