Here is the command to enable it at database level: -To enable Snapshot Isolation (SI)ĪLTER DATABASE AdventureWorks2012 SET ALLOW_SNAPSHOT_ISOLATION ON For RCSI it becomes the default isolation level for all the transactions, whereas you need to specifically specify the SI with the transaction with which you want to use it with the SET command. Whichever snapshot isolation you use, you need to first enable it at a database level. Please refer to my earlier article ( Snapshot Isolation Level in SQL Server – What, Why and How – Part 1) for a basic understanding of isolation levels and snapshot based isolation levels and how they differ from each other in terms of performance and cost. In this article series I discuss what snapshot isolation levels are, their variants, their performance and cost impact, why and when we should use them, and how we should start using this feature. Some people are confused by the two variants of snapshot isolation level (Read Committed Snapshot Isolation (RCSI) and Snapshot Isolation (SI)) and use one variant where the other is needed or vice versa. Others stay away from it because of this extra overhead. Some people use it frequently, as it minimizes blocking and improves performance/concurrency, without knowing its impact on maintaining versions in tempdb. Introduced in SQL Server 2005, Snapshot Isolation levels improve performance, however, there are some caveats to consider when using this feature.
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