Isolation Level Basics

Randolph West describes the primary isolation levels in SQL Server:

There are four isolation levels in SQL Server (as quoted from SQL Server Books Online):

  • Read uncommitted (the lowest level where transactions are isolated only enough to ensure that physically corrupt data is not read)
  • Read committed (Database Engine default level)
  • Repeatable read
  • Serializable (the highest level, where transactions are completely isolated from one another)

Read on for a discussion of what these mean, as well as how optimistic versus pessimistic concurrency (in this case, Read Committed Snapshot Isolation versus Read Committed) comes into play.

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1 Comment

  • Randolph West on 2017-08-03

    I regret not using that terminology in the post, namely optimistic vs pessimistic. Thanks for mentioning it.

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