Update command causing lock in DB.

Hi,

Application team was executing UPDATE statement in DB through Abinitio
graph. When they trigger a job, a session is spawned in DB, in parallel
another session is also spawned and executed the same UPDATE statement.

When I checked the locks in DB, I found that both the sessions are updating
the same record. My concern is how UPDATE causes locking in DB.

Here is how MVCC works. If one session is updating a record, it should
release the lock once it updated the row and other one should be able to
acquire the row lock. Maybe I am wrong, please suggest how to handle this
situation.

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Thanks & Regards
Gambhir Singh