SQL Server Execution Plans - Red Gate Software

Chapter 3: Text and XML Execution
Plans for Basic Queries
Chapter 2 described how to read graphical execution plans, building your understanding
of what operators do and how the data flows from one operator to the next. Learning
how to read graphical execution plans is not wasted time, because what you learned
there also applies to reading text and XML execution plans. While these plans don't have
icons and Property sheets, they consist of the exact same operators and properties; so, by
learning how to read graphical execution plans, you also learn how to read text and XML
execution plans.
In early versions of SQL Server, only text-based execution plans were available and many
people found them hard to read, especially when dealing with complex plans. Microsoft
eventually relented and introduced graphical execution plans in SQL Server 7, in addition
to offering text execution plans. I find graphical execution plans much easier to read than
text plans, and I guess I'm not the only database professional who feels this way, as text
execution plans are on the SQL Server deprecation list and will eventually go away.
In SQL Server 2005, Microsoft modified the internal structure of execution plans. Instead
of the proprietary binary format that they were formerly, now all graphical plans are
actually XML underneath. We can access the XML in all these plans directly. Like textbased
plans, XML plans can be difficult to read and analyze if you look straight at the
raw XML code. So why did Microsoft decide to use XML for execution plans if they are
difficult to read?There are several reasons for the change. Essentially, XML is a common
file format that we can use programmatically, unlike text-based execution plans. This
means you can use XQuery to access data within XML plans. XML plans also provide
a much richer environment to store more execution plan details than ever before. In
addition, XML plans are stored in a portable format that makes them easy to share with
others. For example, I can send an XML plan to a fellow DBA, and she can use SSMS to
graphically display and analyze it or run queries directly against it. Text-based plans, on
the other hand, don't offer any of these benefits.
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