SQL Server Execution Plans - Red Gate Software

Chapter 3: Text and XML Execution Plans for Basic Queries
To most people, an XML plan is simply a common file format in which to store a graphical
execution plan, so that they can share it with other DBAs and developers.
I would imagine that very few people would prefer to read execution plans in the raw
XML format. Having said that, there is one over-riding reason why you will absolutely
want to use the raw XML data as a tool in your toolbox, and that is programmability. You
can run XQuery T-SQL queries against XML files and XML plans. In effect, this gives us a
direct means of querying the plans in the plan cache. This means we can display specific
details of a plan and, by performing a search on specific terms, such as "Index Scan," we
can track down specific, potentially problematic, aspects of a query. We'll see an example
of this a little later.
XML plans can also be used in plan forcing, where we essentially dictate to the query
optimizer that it should use only a specified plan to execute the query. We'll cover this
topic in detail in Chapter 8, but it's worth noting here that, contrary to what you might
hear, plan forcing does not bypass the optimization process.
In the following section, we take a brief look at the structure of XML as it exists behind
graphical plans and in the plan cache.
An estimated XML plan
This section will show the information available to you in an XML plan. Just to get a
sense of the XML structure, you'll follow through this example and "read" the XML in
the same way as you have done previously for graphical and text plans. However, this
example is not representative of how you're really going to use XML execution plans in
your day-to-day work. You won't generally be browsing through the raw XML data in an
attempt to find information.
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