Valid locking levels used by transactions - Oracle Schema

Q.  Which two are the valid locking levels that are used by transactions in an Oracle database?
- Published on 27 Jul 15

a. Row level
b. Block level
c. Object level
d. Schema level
e. Both A & C

ANSWER: Both A & C
 

    Discussion

  • Nirja Shah   -Posted on 28 Sep 15
    Row-Level Locking

    - Both read committed and serializable transactions use row-level locking, and both will wait if they try to change a row updated by an uncommitted concurrent transaction.
    - The second transaction that tries to update a given row waits for the other transaction to commit or undo and release its lock.
    - If that other transaction rolls back, the waiting transaction, regardless of its isolation mode, can proceed to change the previously locked row as if the other transaction had not existed.
    - However, if the other blocking transaction commits and releases its locks, a read committed transaction proceeds with its intended update.
    - A serializable transaction, however, fails with the error cannot serialize access error, because the other transaction has committed a change that was made since the serializable transaction began.

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