The process of cleaning
up the resulting mess is called instance recovery or crash recovery.
What Is Instance Recovery?
When yourestart an Oracle instance after a failure, Oracle detects that a crash
occurred using information in the control file and the headers of the database files.
Oracle then performs instance recovery automatically and uses the online redo logs
to guarantee that the physical database is restored to a consistent state as it existed at
the time of the crash. This includes two actions:
??? All committed transactions will be recovered.
??? In-flight transactions will be rolled back or undone.
Note that an in-flight transaction might be one that a user didn??™t commit or one that
was committed by the user but not confirmed by Oracle before the system failure. A
transaction isn??™t considered committed until Oracle has written the relevant details
Telltale Error Messages
The following two error messages are often good indicators that an Oracle instance is
down:
ORA-03113: End-of-file on communication channel
This message is usually received by clients that try to resubmit an operation that failed
due to an instance failure.
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