Adding indexes to reduce contention

An update or delete statement that has no useful index on its search arguments performs a table scan and holds an exclusive table lock for the entire scan time. If the data modification task also updates other tables:

Creating a useful index for the query allows the data modification statement to use page or row locks, improving concurrent access to the table. If creating an index for a lengthy update or delete transaction is not possible, you can perform the operation in a cursor, with frequent commit transaction statements to reduce the number of page locks.