An update lock is taken by the DBMS when data must first be read before it is changed or deleted.
– The update lock indicates that the data be modified or deleted in the future.
– If the data is actually modified or deleted, the DBMS will promote the update lock to an exclusive lock.
– If an update lock has taken on a row, page, or table, other processes or users generally are permitted to read the data, but not to modify it.