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  • Compute Scalars, Expressions and Execution Plan Performance

    The humble Compute Scalar is one of the least well-understood of the execution plan operators, and usually the last place people look for query performance problems.  It often appears in execution plans with a very low (or even zero) cost, which goes some way to explaining why people ignore it. Some readers will already know that a Compute ...
    Posted to Paul White: Page Free Space (Weblog) by Paul White on September 4, 2012
  • Fooling the Query Optimizer

    Did you ever wanted to know which execution plans the Query Optimizer would generate for your queries should your tables have millions of records? You can actually generate those plans by using the undocumented ROWCOUNT and PAGECOUNT options of the UPDATE STATISTICS statement. These options can be used on small or empty tables and can be ...
    Posted to Benjamin Nevarez (Weblog) by Ben Nevarez on January 13, 2010
  • Database Engine Tuning Advisor and the Query Optimizer

    Did you know that the Database Engine Tuning Advisor (DTA) uses the Query Optimizer to help you to create indexes, indexed views, and partitions for your databases? The DTA uses the Query Optimizer to estimate the cost of queries so it can select the choices with the lowest estimated cost. But, how can the Query Optimizer estimate the cost of a ...
    Posted to Benjamin Nevarez (Weblog) by Ben Nevarez on November 11, 2009
  • The Missing Indexes Feature

    Since I will be speaking about the Query Optimizer at the coming PASS Summit, I have been preparing my presentation and at the same time blogging about it. This time I will describe the Missing Indexes feature, seen from the point of view of the Query Optimizer.   We know that it is the job of the Query Optimizer to find an efficient ...
    Posted to Benjamin Nevarez (Weblog) by Ben Nevarez on September 25, 2009
  • How the Query Optimizer Uses Statistics

      This post shows how the Query Optimizer uses statistics to estimate the selectivity of expressions during query optimization.   You can also use this as a second part of my last post, The Query Optimizer and Parameter Sniffing. Here I will show you the advantage of the use of statistics when the Query Optimizer can “sniff” the ...
    Posted to Benjamin Nevarez (Weblog) by Ben Nevarez on September 3, 2009
  • The Query Optimizer and Parameter Sniffing

      As we all know, the SQL Server Query Optimizer uses statistics to estimate the cardinality and selectivity of predicates of a query to produce an optimal execution plan. The Query Optimizer accomplishes this by first inspecting the values of the query parameters. This behavior is called parameter sniffing and it is a good thing. Getting an ...
    Posted to Benjamin Nevarez (Weblog) by Ben Nevarez on August 27, 2009
  • The Query Optimizer and Computed Columns

    In my previous post I talked about contradiction detection as one of the early steps in query optimization. Another interesting step performed during query optimization is the automatic matching of computed columns. Although computed columns have been available in previous versions of SQL Server, the automatic matching feature was introduced until ...
    Posted to Benjamin Nevarez (Weblog) by Ben Nevarez on August 10, 2009
  • The Query Optimizer and Contradiction Detection

    One of the many interesting topics I found while working as technical editor of the SQL Server 2008 Internals book was the concept of contradiction detection. So, in this post I will to try to expand on this topic and provide some additional examples.     Contradiction detection is performed by SQL Server during the early steps of the ...
    Posted to Benjamin Nevarez (Weblog) by Ben Nevarez on August 4, 2009
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