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Locks (Transaction isolation levels (read uncommitted ((S) locks not…
Locks
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Types
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Intended
Example: update a row and have two intent exclusive (IX) locks just indicate that there is the child object (row) with exclusive lock held.
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Examples
Imagine we have the session that held exclusive (X) lock on the single row. In another session, we are trying to update a different row running a nonoptimized update statement that introduces the scan. SQL Server would acquire update (U) lock on every row it is scanning and eventually would be blocked trying to read the row with exclusive (X) lock held. It does not matter that we want to update a completely different row—SQL Server still need to acquire update (U) lock on the rows it scan to evaluate if they need to be updated.