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At
this point, users can no longer access the database.
2. Dismounting the database. The Oracle instance dismounts the database. Oracle
updates the relevant entries in the control files to record a clean shutdown and then
closes them. At this point, the entire database is closed; only the instance remains.
3. Shutting down the instance. The Oracle software stops the background processes
of the instance and frees, or deallocates, the shared memory used for the SGA.
70 | Chapter 3: Installing and Running Oracle
In some cases (e.g., if there is a machine failure or the DBA aborts the instance), the
database may not be closed cleanly. If this happens, Oracle doesn??™t have a chance to
write the modified database blocks from the SGA to the datafiles. When Oracle is
started again, the instance will detect that a crash occurred and will use the redo logs
to automatically perform what is called crashrecovery . Crash recovery guarantees
that the changes for all committed transactions are done and that all uncommitted or
in-flight transactions will be cleaned up.


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