SQL Server Execution Plans - Red Gate Software

Chapter 1: Execution Plan Basics
• changing the structure or schema of temporary tables used by the query
• changes to dynamic views used by the query
• changes to cursor options within the query
• changes to a remote rowset, like in a distributed partitioned view
• when using client-side cursors, if the FOR BROWSE options are changed.
Clearing Plans from the Plan Cache
Since the cache plays such an important role in how execution plans operate, you need a
few tools for querying and working with the plan cache. First off, while testing, you may
want to see how long a plan takes to compile, or to investigate how minor adjustments
might create slightly different plans. To clear the cache, run this:
DBCC FREEPROCCACHE
Listing 1.2
WARNING: Clearing the cache in a production environment
Running Listing 1.2 in a production environment will clear the cache for all databases on the server. That
can result in a significant performance hit because SQL Server must then recreate every single plan stored
in the plan cache, as if the plans were never there and the queries were being run for the first time ever.
While working with an individual query, it's usually better to target that query to remove
just it from the plan cache. You can use DBCC FREEPROCCACHE and pass either the
sql_handle or plan_handle to remove just the referenced plan. The plan_handle
and sql_handle are available from various DMO objects (see the section on DMOs).
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