Roy Ernest Database Administrator Pinnacle Sports Worldwide

Contents What is Row level Versioning How it works What uses it? Conclusion Costs of using RLV May 27, 20102Curaçao SQL Server User Group

What is Row Level Versioning In Computing terms Version means a number indicating which revision something is. Versioning works by making any transaction that changes data keep the old versions of the data around so that a 'snapshot' of the database (or a part of the database) can be constructed from these old versions. Version records need to be kept in the version store only as long as there are there are operations that might require them. May 27, 20103Curaçao SQL Server User Group

What it uses. Snapshot Isolation (SI) Read Committed Snapshot Isolation (RCSI) May 27, 20104Curaçao SQL Server User Group These isolation levels let the Select get the previously committed value of the row without causing any blocking.

May 27, 20105Curaçao SQL Server User Group SQL Server keeps previously committed value when it gets updated. Chance of multiple versions of same row to be maintained. Uses TempDB to store the versions. How it works

Test and see if it works. May 27, 20106Curaçao SQL Server User Group Create a test DB Set two Isolation Levels Create test objects, data Test the versioning

What uses RLV Technology Triggers Online Index Creation Multiple Active Result Sets May 27, 20107Curaçao SQL Server User Group

Advantages of RLV No Lock when Selecting Select gives the last committed data Decreases chances of Dead Lock Lock Escalation is reduced Not many locks used, thus reduces the load on Server May 27, 20108Curaçao SQL Server User Group

Cost due to RLV Since versions are kept, increased use of resources Higher IO, CPU, Mem Usage when doing Updates and Deletes TEMPDB must have more space to handle versions 14 bytes will be added to the row in the DB to keep track of versions Long version chain can affect Data read performance May 27, 20109Curaçao SQL Server User Group

May 27, Curaçao SQL Server User Group

Additional Resources Technet Article by Roy Ernest May 27, 2010Curaçao SQL Server User Group11

May 27, Curaçao SQL Server User Group