drop materialized view hung !!!

Cause: when you drop the materialized view ,then oracle will to check the integrity of the materilized view , if the mview is created referencing remote object by db-link. then Oracle will access the remote object.

Sometimes the db-link is expired, So when you drop mview at the moment, the process will hung and the wait events would be "single-task message" and "enq: TM-contention" .

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