Transactions and Locking

SQL Server issues and holds onto locks for the duration of a transaction to ensure the isolation and consistency of the modifications. Data modifications that occur within a transaction will acquire exclusive locks, which are then held until the completion of the transaction. Shared locks, or read locks, are held for only as long as the statement needs them; usually, a shared lock is released as soon as data has been read from the resource (row, page, table). The length of time a shared lock is held can be modified by the use of keywords such as HOLDLOCK in a query. If this option is specified, shared locks are held onto until the completion of the transaction.

What this means for database application developers is that ...

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