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Data & Analytics · Intermediate

Locking

The mechanism that controls concurrent access by placing shared (read) or exclusive (write) locks on resources.

Definition

Shared locks allow concurrent reads, while exclusive locks block other readers and writers. Locks can be taken at row, page or table level, and many row locks may escalate to a table lock. Locks held too long cause blocking.

Exam tip

Exclusive and shared locks are incompatible; that incompatibility is what causes blocking.

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