Solution

The correct answer is tb can lock d in intention-shared (IS) mode.

Key Points

• A transaction holding a lock in shared and intention-exclusive (SIX) mode indicates that it has a shared lock on the data item and may acquire exclusive locks on specific sub-resources.
• Other transactions are allowed to acquire intention-shared (IS) locks on the same data item, as this does not conflict with the existing lock.
• However, no other transaction can acquire shared (S), exclusive (X), or intention-exclusive (IX) locks on the same data item, as these would conflict with the SIX lock.

Additional Information

• Lock Compatibility Matrix:
  • SIX Lock: A SIX lock is compatible only with IS locks from other transactions.
  • IS Lock: Used to indicate that a transaction intends to acquire shared locks on sub-resources.
  • IX Lock: Indicates intent to acquire exclusive locks on sub-resources.
  • S Lock: Provides shared access to a resource but prevents exclusive access by others.
  • X Lock: Provides exclusive access to a resource and prevents any other locks.
• Conflict Rules:
  • If a transaction holds a SIX lock, it prevents any other transaction from acquiring S, X, or IX locks on the same data item.
  • However, IS locks are allowed as they do not interfere with the shared component of the SIX lock.