Performance Tuning with SQL Server Dynamic Management Views

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Chapter 3: Query Plan Metadata
Each plan has 1-to-N queries and in this section we're going to explore how to get
detailed information about the individual queries in the batch or object. To get these
query statistics, be it for a standalone query or a query within a larger stored procedure
or prepared statement, we use the sys.dm_exec_query_stats DMV.
The sys.dm_exec_query_stats DMV will return one row per query that is executed
within a batch or stored procedure, and provides columns such as total_worker_time
(CPU), total_physical_reads, total_logical_reads, which can give you a very
useful overview of the system resources that your queries are eating up.
Pre-SQL Server 2005, the only way to get this sort of information was through Profiler.
However, Profiler only lets you collect the information as the queries occur, not after the
event. Now, the next time you hear about a problem second-hand, while walking down
the hallway, which is too often how users report problems, you'll be able to interrogate
the sys.dm_exec_query_stats DMV and find out what happened. This is an
exciting step forward for most DBAs, especially given that resorting to Profiler after the
event often entailed capturing traces over long periods of time, in order to reobserve the
problem, and this could be really costly in terms of server resources and programmer
sanity, since doing the matching of query text after the fact is very difficult.
Overview of sys.dm_exec_query_stats
The sys.dm_exec_query_stats DMV contains quite a few columns that are
incremented counters, and provide information about how many times a query has been
executed and the resources that were used. It is described in Books Online as follows:
Returns aggregate performance statistics for cached query plans. The view contains one row per query
statement within the cached plan, and the lifetime of the rows is tied to the plan itself. When a plan is
removed from the cache, the corresponding rows are eliminated from this view.