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Oracle SQL Transactions and Concurrency Control Flashcards

7 cards from real Oracle SQL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Oracle SQL Transactions and Concurrency Control flashcards as text

  1. What is the default transaction isolation level in Oracle Database?

    Answer: READ COMMITTED

    Oracle's default isolation level is READ COMMITTED, where each query sees only data that was committed before the query began.

  2. Which read phenomenon is prevented by Oracle's READ COMMITTED isolation level?

    Answer: Dirty reads

    READ COMMITTED prevents dirty reads because queries only see data that was committed before the query started, never uncommitted data from other transactions.

  3. What does a dirty read mean in the context of database transactions?

    Answer: Reading uncommitted data from another transaction that may later be rolled back

    A dirty read occurs when a transaction reads data modified but not yet committed by another transaction, which may be rolled back, making the read data invalid.

  4. Which Oracle SQL statement correctly sets the current transaction's isolation level to SERIALIZABLE?

    Answer: SET TRANSACTION ISOLATION LEVEL SERIALIZABLE

    SET TRANSACTION ISOLATION LEVEL SERIALIZABLE must be the first statement in a transaction and sets the isolation level for that transaction only.

  5. What is a phantom read in the context of database transactions?

    Answer: A transaction re-executes a range query and finds new rows inserted and committed by another transaction since the first execution

    A phantom read occurs when a transaction re-executes a range query and finds new rows ('phantoms') inserted and committed by another transaction since the first execution.

  6. What does SET TRANSACTION READ ONLY accomplish in Oracle SQL?

    Answer: Starts a transaction that can only SELECT and sees a consistent data snapshot as of the transaction start time

    SET TRANSACTION READ ONLY starts a read-only transaction that sees a consistent snapshot of data as of the transaction's start time, and prevents any DML within that transaction.

  7. What is the primary purpose of the UNDO tablespace in Oracle in relation to transactions?

    Answer: To store before-images of changed data, enabling ROLLBACK operations and read-consistent snapshots

    The UNDO tablespace stores before-images (old versions) of changed data, enabling Oracle to roll back transactions and provide MVCC read-consistent snapshots to other sessions.