performance - What is a Bookmark Lookup in Sql Server? -


I am trying to customize a query that looks at historical data. I am using Query Analyzer to see the execution plan and I have found that most of my query costs are called "bookmarks loopup" I have never seen this node in this execution plan and I do not know what it means is.

Is this a good thing or a bad thing in a query?

A process of finding actual data in the SQL table, based on the entry found in a non-clustered index The box is lookup.

When you search for a value in a non-clustered index, and you need more fields than the part of your query index lead node (all index fields, plus any possible inclusion columns) , Then the SQL server needs to retrieve the actual data page (s) - which is called bookmarks lookup.

In some cases, this is actually the only way to go - if your query only requires one more field ('not completely'), then that field is in non-cluster It may be a good idea to include the index. In that case, the non-clustered index will contain all the fields needed to complete your query (an "overlay" index) in the Pan-level node, and thus a bookmarks lookup will no longer be necessary.

Mark


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