Exclusives locks are required when modifications are going to be made. This can include INSERT, UPDATE or DELETE. Shared locks are for reads. Peple talk about the locks being "converted" but that's not accurate. What happens is a shared lock is in place while reads are being done to find the right row, for an UPDATE as an example. Then, when the right row is found, an exclusive lock will be placed, usually in addition to the shared lock, to update the data.
answered Apr 23 '12 at 05:29 PM
Grant Fritchey ♦♦