<< Click to Display Table of Contents >> Navigation:  Application development > Database driver characteristics > SQL drivers > SQL table-locking behavior

The SQL driver provides a degree of support for table locking if the SQL server supports it. Different SQL servers provide different levels of support for table locking. Some servers provide no table locking support at all. Others only provide support for read-only locking (many clients can share a lock and all can read). Some SQL servers provide support for locking, but require the client to wait until a lock is granted, rather than letting the client know immediately if the lock could not be achieved. For information on locking support provided by your SQL server, see your server documentation.

SQL servers that support table locks maintain a lock within the context of a transaction: a lock can only be acquired within a transaction, and only released by terminating the transaction. This is sometimes referred to as a two-phase locking protocol. When the SQL driver is asked to acquire a table lock, it automatically starts a transaction if necessary. When asked to release a table lock, the SQL driver must commit the transaction in order to release the lock. Because a transaction commit releases all locks, the SQL driver automatically re-acquires any remaining locks.