A deadlock is a condition where two or more users are waiting for data locked by each other. Oracle automatically detects a deadlock and resolves them by rolling back one of the statements involved in the deadlock, thus releasing one set of data locked by that statement. Statement rolled back is usually the one which detects the deadlock.
Deadlocks are mostly caused by explicit locking because oracle does not do lock escalation and does not use read locks. Multitable deadlocks can be avoided by locking the tables in same order in all the applications, thus precluding a deadlock.
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