sql server 2005 row level versioning

Roy Ernest

Database AdministratorPinnacle Sports Worldwide

[email protected]

ContentsWhat is Row level Versioning How it worksWhat uses it?ConclusionCosts of using RLV

May 27, 2010 2Curaçao SQL Server User Group

What is Row Level VersioningIn 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.


What it uses.Snapshot Isolation (SI)Read Committed Snapshot Isolation (RCSI)


These isolation levels let the Select get the previously committed value of the row without causing any blocking.


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.


Create a test DBSet two Isolation LevelsCreate test objects, dataTest the versioning

What uses RLV Technology

TriggersOnline Index CreationMultiple Active Result Sets


Advantages of RLV

No Lock when SelectingSelect gives the last committed dataDecreases chances of Dead LockLock Escalation is reducedNot many locks used, thus reduces the load on Server


Cost due to RLV

Since versions are kept, increased use of resourcesHigher IO, CPU, Mem Usage when doing Updates and

DeletesTEMPDB must have more space to handle versions14 bytes will be added to the row in the DB to keep

track of versionsLong version chain can affect Data read performance


Additional Resources

Technethttp://technet.microsoft.com/en-us/library/ms189050.aspx

Article by Roy Ernesthttp://www.sqlservercentral.com/articles/SQL+Server+2005/62464/#

May 27, 2010 Curaçao SQL Server User Group 11

sql server 2005 row level versioning

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