pessimistic-locking - w3toppers.com

SQL Server, the misleading XLOCK & optimizations

Exclusivity of X locks vs U locks In the lock compatibility matrix below it can be seen that the X lock is only compatible with the schema stability and Insert Range-Null lock types. U is compatible with the following additional shared lock types S/IS/RS-S/RI-S/RX-S lock compatibility matrix http://i.msdn.microsoft.com/ms186396.LockConflictTable(en-us,SQL.105).gif Granularity of X locks These are taken … Read more

Optimistic vs. Pessimistic locking

Optimistic Locking is a strategy where you read a record, take note of a version number (other methods to do this involve dates, timestamps or checksums/hashes) and check that the version hasn’t changed before you write the record back. When you write the record back you filter the update on the version to make sure … Read more