Sunday, December 21, 2008

Link Servers

When you create a link between two SQL Servers, SQL Server does its best to perform as much work as it can on the remote server. This way, less data has to be moved from the remote server to the local server, helping to reduce overhead and boosting performance. But for some particular operations, they have to be performed on the local server, not the remote server. Some examples of locally performed operations include:

* Data conversion operations
* Queries that use the bit, timestamp, or uniqueidentifier data types
* Queries that use the TOP clause

Because of this, you may want to try to avoid performing any of the above operations using a remote linked server.

If you are running a remote query against a linked server, and you want to find out which parts are performing on the remote server and which are performing on the local server, run the query from Query Analyzer or Management Studio and take a look at the query plan. It will tell you what part of your query is running where. It should be your goal to create code that runs mostly on the remote server, not the local server. [7.0, 2000, 2005]

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