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ORA-27100: shared memory realm already exists

by Snehashish Ghosh

Scenario


 After increase in the value of SGA_MAX_SIZE from 1500M to 2G to accommodate future database growth requirement without a restart of the database instance the following issue has been encountered:

ORA-27100: shared memory realm already exists is reported during a manual startup of the database .
SQL> startup

ORA-27100: shared memory realm already exists

SQL> shutdown immediate
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
SQL>

Restarting the Oracle service, the same error is encountered.
Rebooting the database server machine does not help as well to free some memory for oracle (because that also restarts the service).

The actual root cause is in fact the limitation of physical memory.
When the service is not restarted but the instance is stopped and r...

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