When you update, delete, or create a record, an ODBC data source puts an exclusive lock on the record; however, the data source does not apply the exclusive lock to a record until all shared locks on it are released. Therefore, you cannot perform an update on a record until other users release it. If a record has an exclusive lock on it, no other user can access it until it is released at the end of a transaction. In a transaction block, the data source always holds an exclusive lock until the end of a transaction's scope if the data-source driver supports commitment control boundaries and the ODBC AUTOCOMMIT feature is not turned on.
Exclusive locking significantly affects the performance of data sources that use page-level locking, especially if the transaction requires a large number of exclusive locks on non-contiguous records.
