Updating views sql server
Once the transaction that holds the update lock is ready to change the data, the update lock (U) will be transformed to an exclusive lock (X).
It is important to understand that update lock is asymmetrical in regards of shared locks.
While objects are locked, SQL Server will prevent other transactions from making any change of data stored in objects affected by the imposed lock.
When a bulk update lock is acquired, other processes will not be able to access a table during the bulk load execution.Translated into the SQL Server language, this means that when a transaction imposes the lock on an object, all other transactions that require the access to that object will be forced to wait until the lock is released and that wait will be registered with the adequate wait type SQL Server locks can be specified via the lock modes and lock granularity Lock mode considers various lock types that can be applied to a resource that has to be locked: for the transaction that imposed the exclusive lock, as long as the transaction holds the lock.The exclusive lock will be imposed by the transaction when it wants to modify the page or row data, which is in the case of DML statements DELETE, INSERT and UPDATE.However, a shared lock can be imposed by several transactions at the same time over the same page or row and in that way several transactions can the ability for data reading since the reading process itself will not affect anyhow the actual page or row data.In addition, a shared lock will allow write operations, but no DDL changes will be allowed Update lock (U) – this lock is similar to an exclusive lock but is designed to be more flexible in a way.
While the update lock can be imposed on a record that has the shared lock, the shared lock cannot be imposed on the record that already has the update lock Intent locks (I) – this lock is a means used by a transaction to inform another transaction about its to acquire a lock.