If a transaction ta holds a lock on some data item d in shared and…

2026

If a transaction ta holds a lock on some data item d in shared and intention-exclusive (SIX) mode, then which of the following is true for another transaction tb?

  1. tb can lock d in shared (S) mode

  2. tb can lock d in exclusive (X) mode

  3. tb can lock d in intention-exclusive (IX) mode

  4. tb can lock d in intention-shared (IS) mode

  1. A.

    1

  2. B.

    2

  3. C.

    3

  4. D.

    4

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Show answer & explanation

Correct answer: D

The SIX (Shared + Intention Exclusive) lock mode grants shared access to the data item while indicating an intention to acquire exclusive locks on descendant items in a hierarchy.

According to standard lock compatibility matrices, an existing SIX lock is strictly compatible only with the Intention-Shared (IS) mode held by other transactions on the same item.

Locks in Shared (S), Exclusive (X), or Intention-Exclusive (IX) modes conflict with the SIX lock due to incompatible access intents, leaving IS as the only permissible option for transaction t b.

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