Many times Oracle DBA's are often faced with situation where shutting down the instance with shutdown immediate seems to take infinite time and gives an impression that the session in hung. In most of the cases this is not a hang. Hang can be defined as a scenario when few sessions/processes are waiting on some action and in turn blocking other session/processes to complete their tasks. Now the original sessions could be waiting because of resource issues or Oracle Bugs. Shutdown immediate can take long time to complete (appear to be hung) because of three reasons: Uncommitted transactions are being rolled back. SMON is cleaning temp segments or performing delayed block clean-outs. Processes still continue to be connected to the database and do not terminate. 1. Uncommitted transactions are being rolled back: This is the case when the message 'Waiting for smon to disable tx recovery' is posted in the alert log after we issue shutdown immediate. There ...
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