Performance Tuning with SQL Server Dynamic Management Views

Chapter 2: Connections, Sessions and Requests
expensive queries to the sessions, connections and users that own them. All of this is
accomplished via the following DMOs, which belong to the "Execution-related" category
of objects, and therefore all start with sys.dm_exec_.
• sys.dm_exec_connections – provides information about network traffic and
protocols, as well as user attributes from the calling source of the connection.
Additional details are available from Microsoft Books Online: http://msdn.microsoft.com/en-us/library/foo6bd46fe1-417d-452d-a9e6-5375ee8690d8.aspx.
• sys.dm_exec_sessions – returns information about each user and internal system
session on a SQL Server instance including session settings, security, and cumulative
CPU, memory, and I/O usage. More on this DMV is available from Microsoft Books
Online: http://msdn.microsoft.com/en-us/library/ms176013.aspx.
• sys.dm_exec_requests – provides a range of query execution statistics, such
as elapsed time, wait time, CPU time, and so on. It returns one row for every query
currently executing. More information about this DMV is available in the following
Microsoft KB: http://technet.microsoft.com/en-us/library/ms177648(SQL.90).
aspx.
• sys.dm_exec_sql_text – returns the text of the SQL batch identified by a
sql_handle; see http://msdn.microsoft.com/en-us/library/ms181929.aspx.
• sys.dm_exec_query_plan – returns, in XML format, the query plan, identified by a
plan_handle, for a SQL batch (this DMO is covered in more detail in Chapter 3).
Of course, the journey does not end there. In Chapter 3, we'll delve deeper into query
execution and, in particular, into the execution plans that SQL Server generates, stores
and, hopefully, reuses, during this process. This allows a broader analysis of your query
workload, from the point of view of what is in the plan cache, rather than just those
queries that are executing right now. In Chapter 4, we'll step down to an even lower
granularity, to look at the transactions that are initiated once a query is assigned a plan
and sent on to the engine for processing. Transactions do (hopefully) complete and
requests are fulfilled, yet the associated user can, and usually does, still maintain
connectivity to the SQL Server instance.
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