Testing today Curious. My SID has changed from 1234 to 6789 sometime between 09:56 and 11:28. I've verified that no instance in the cluster has been restarted. I had issued NO commands from this SQLPlus session. The TNS connect-string I use is a simple connect string specifying the SCAN address. So, my session has been migrated maybe from instance 1 to instance 2 or 3 and then back to instance 1 in that 1.5 hours (while it was idle) ? Was it migrated because the service was migrated ? I think I can discount server-side TAF because no instance was restarted. Note : I am a user, not a DBA in this database. SQL> set time on 09:55:08 SQL> select instance_number from v$instance; INSTANCE_NUMBER --------------- 1 1 row selected. 09:55:14 SQL> select distinct sid from v$mystat; SID ---------- 1234 1 row selected. 09:55:22 SQL> select sid, serial# from v$session where sid=1234; SID SERIAL# ---------- ---------- 1234 28693 1 row selected. 09:55:33 SQL> select failover_type, failover_method, failed_over from v$session where sid=1234; FAILOVER_TYPE FAILOVER_M FAI ------------- ---------- --- SELECT BASIC NO 1 row selected. 09:56:35 SQL> 11:28:13 SQL> select instance_number from v$instance; INSTANCE_NUMBER --------------- 1 1 row selected. 11:28:23 SQL> select distinct sid from v$mystat; SID ---------- 6789 1 row selected. 11:28:32 SQL> select sid, serial# from v$session where sid=1234; SID SERIAL# ---------- ---------- 1234 28693 1 row selected. 11:28:43 SQL> select sid, serial# from v$session where sid=6789; SID SERIAL# ---------- ---------- 6789 3281 1 row selected. 11:29:07 SQL> select failover_type, failover_method, failed_over from v$session where sid=1234; FAILOVER_TYPE FAILOVER_M FAI ------------- ---------- --- SELECT BASIC NO 1 row selected. 11:29:18 SQL> select failover_type, failover_method, failed_over from v$session where sid=6789; FAILOVER_TYPE FAILOVER_M FAI ------------- ---------- --- SELECT BASIC YES 1 row selected. 11:29:26 SQL> ---------- Forwarded message ---------- From: Hemant K Chitale <hemantkchitale@xxxxxxxxx> Date: Sun, Jun 16, 2013 at 10:38 PM Subject: Session migrated to another instance To: ORACLE-L <oracle-l@xxxxxxxxxxxxx> How is this done ? At 17:11, my sqlplus session was connected to instance 3 in the RAC cluster. At 17:53, the session is on instance 1. No explicit commands issued from the client. Disclaimer : In this case I am a *user* not the DBA. SQL> set time on 17:11:44 SQL> select sys_context('USERENV','INSTANCE') from dual; SYS_CONTEXT('USERENV','INSTANCE') ---------------------------------------------------------------------------- -- 3 1 row selected. 17:11:47 SQL> select sys_context('USERENV','SID') from dual; SYS_CONTEXT('USERENV','SID') ---------------------------------------------------------------------------- -- 3118 1 row selected. 17:11:49 SQL> select sys_context('USERENV','INSTANCE') from dual; SYS_CONTEXT('USERENV','INSTANCE') ---------------------------------------------------------------------------- -- 1 1 row selected. 17:53:38 SQL> select sys_context('USERENV','SID') from dual; SYS_CONTEXT('USERENV','SID') ---------------------------------------------------------------------------- -- 1272 1 row selected. 17:53:42 SQL> -- Hemant K Chitale http://hemantoracledba.blogspot.com -- Hemant K Chitale http://hemantoracledba.blogspot.com http://hemantscribbles.blogspot.com http://web.singnet.com.sg/~hkchital -- //www.freelists.org/webpage/oracle-l