SQL Server Execution Plans - Red Gate Software

Chapter 3: Text and XML Execution Plans for Basic Queries
The simple example in Listing 3.18 returns a list of operators within queries currently
stored in the plan cache. It illustrates how we can construct queries against the plan
cache, using the DMVs, but I would still hesitate before running this query on a
production system if that system was already under stress. Exercise caution using these
XML queries.
SELECT TOP 3
RelOp.op.value('declare default element namespace "http://schemas.
microsoft.com/sqlserver/2004/07/showplan";
@PhysicalOp', 'varchar(50)') AS PhysicalOp,
dest.text,
deqs.execution_count,
RelOp.op.value('declare default element namespace "http://schemas.
microsoft.com/sqlserver/2004/07/showplan";
@EstimatedTotalSubtreeCost', 'float') AS EstimatedCost
FROM sys.dm_exec_query_stats AS deqs
CROSS APPLY sys.dm_exec_sql_text(deqs.sql_handle) AS dest
CROSS APPLY sys.dm_exec_query_plan(deqs.plan_handle) AS deqp
CROSS APPLY deqp.query_plan.nodes('declare default element namespace
"http://schemas.microsoft.com/sqlserver/2004/07/showplan";
//RelOp') RelOp (op)
ORDER BY deqs.execution_count DESC
Listing 3.18
This query returns the first three operators from the most frequently called query in
the plan cache. The basic construct is easy enough to follow. In the FROM clause, three
DMVs are referenced, sys.dm_exec_query_stats, sys.dm_exec_sql_text, and
sys.dm_exec_query_plan, along with a reference to the query_plan column
within sys.dm_exec_query_plan and to the .nodes of the XML. Apart from that,
it's all XQuery. The results from my system look as shown in Figure 3.10.
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