Lock Compatibility in SQL Server

Pubblicato il: 01 maggio 2017
sul canale di: IT Port
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Lock compatibility controls whether multiple transactions can acquire locks on the same resource at the same time. If a resource is already locked by another transaction, a new lock request can be granted only if the mode of the requested lock is compatible with the mode of the existing lock. If the mode of the requested lock is not compatible with the existing lock, the transaction requesting the new lock waits for the existing lock to be released or for the lock timeout interval to expire.For example, no lock modes are compatible with exclusive locks. While an exclusive (X) lock is held, no other transaction can acquire a lock of any kind (shared, update, or exclusive) on that resource until the exclusive (X) lock is released. Alternatively, if a shared (S) lock has been applied to a resource, other transactions can also acquire a shared lock or an update (U) lock on that item even if the first transaction has not completed. However, other transactions cannot acquire an exclusive lock until the shared lock has been released.


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