oracle database login

what happened when logging into oracle datrabase ?:

1. A new Oracle process is started (either by the listener or by local sqlplus if using the local BEQ connection)
2. The new process attaches to SGA shared memory segments (so it could access all the needed SGA structures)
3. The new process allocates process and session state objects and initializes new session structures in SGA

login as below if normal login stuck:

sqlplus -prelim "/ as sysdba"


 -prelim option stands for "preliminary connection;
it only do step 1 and 2 compared to normal login so it will not be stuck by oracle latch contention. However you can not query normal table and even v$ views but run oradebug command.

reference:

http://tech.e2sn.com/oracle/troubleshooting/hang/how-to-log-on-even-when-sysdba-can-t-do-so