enq: TM - contention

PROBLEM:
One of user session is running for a long time without return.

CAUSE:
The running session is waiting on event: enq: TM - contention. The table is locked by another session.

SOLUTION:
1. Log out of blocking session if task is completed.
2. create a index for foreign key column if it is related to lock parent table.


reference:
http://www.confio.com/logicalread/solving-oracle-enq-tm-contention-wait-events/