http://www.sqlservercentral.com/blogs/steve_jones/2011/01/17/isolation-levels_1320_mcm-prep/

Printed 2014/10/25 12:05AM

Isolation Levels–MCM Prep

By Steve Jones, 2011/01/17

I was watching the Isolation Levels video for my MCM prep and learned something about the isolation levels. I knew there were four levels, but I hadn’t realized that SQL Server used the default of level 1, out of the 4 ANSI levels. The levels are:

You can read more about them here, but what I learned was that these levels are actually organized in a logical manner. If you look at it this way, the levels can also be described as:

The flip side of the greater data integrity is that more locks are needed, and held longer as you move up the levels. That can impact concurrency.

As with everything in databases, there is a tradeoff.

Note that SQL Server allows you to actually get around some of these issues with row level versioning. Of course, this isn’t free. It comes at the expense of space in tempdb.


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