Got the following question from a colleague:

We have a table with allpages lock scheme. A nonclustered index is added to this table (which has millions of entries). During the creation of the index, many blocked delete commands are observed. Would having another lock scheme (data page lock or data row lock) help ?

Answer:

The locking scheme of the table doesn’t matter in this case. When an index is created, a table lock is always created. If the index is clustered, then the lock is exclusive i.e. SELECT, INSERT, UPDATE and DELETE operations are blocked. Otherwise it is only a shared lock i.e. INSERT, UPDATE and DELETE statements are still blocked but SELECT statement are not blocked. In this case it is a nonclustered index but for a DELETE statement it makes no difference, the statement is still blocked.