A common misconception I've encountered in talking with numerous DBAs is that "reducing the number of reads a query performs is an important aspect of improving its performance". These are in fact the only true performance metrics available for a SQL Server trace event. The most common data columns used for this purpose are Duration, CPU, Writes and Reads. I am sure you have all used SQL traces to evaluate the performance of queries and batches. In this article, we will examine this counter's true meaning and provide examples that prove it can sometimes be quite misleading. SQL Server trace, the most common tool DBAs use to evaluate query performance, provides the 'logical reads' counter on which many DBAs rely for evaluating a query's I/O performance.
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