Cause
Attempted to shrink MEMORY_TARGET to the specified value but did not succeed because the PGA and SGA components could not be shrunk.
Attempted to shrink MEMORY_TARGET to the specified value but did not succeed because the PGA and SGA components could not be shrunk.
Do not set MEMORY_TARGET to a value below the current value without first shrinking the individual memory components.
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/e0.htm
https://community.oracle.com/message/10539829
https://community.oracle.com/message/9451750
https://community.oracle.com/message/3376229
https://community.oracle.com/message/4322063
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