Performance tuning and troubleshooting in SQL Server can often be a challenging task. With a wide range of tools available, such as Profiler, Perfmon, DBCC commands, and stored procedures, it can be difficult to determine which tool to use for a specific issue. Additionally, some tools may impact performance themselves, making them less than ideal for certain situations. Furthermore, there are undocumented DBCC commands and system tables that should only be used by experienced professionals or under the guidance of Microsoft support.
However, SQL Server 2005 introduced a game-changing feature called Dynamic Management Objects (DMO). DMO provides a transparent view into the inner workings of SQL Server, making it easier to diagnose and troubleshoot performance issues. There are two types of DMO: Dynamic Management Views (DMV) and Dynamic Management Functions (DMF). These objects generate tabular result sets with dynamically generated information about the state and health of the server.
There are 75 fully documented dynamic management views and functions in SQL Server Books Online. These objects collect information from various sources within the engine, allowing you to query them using simple SELECT statements. It’s important to note that the information collected by DMOs is only available while the server is running, as it is reset upon restart.
The DMOs are categorized based on their functionality, making it easy to find and distinguish them. For example, the prefix “dm_io_” is used for objects related to disk and network I/O, while “dm_db_” is used for database-related objects. Other categories include “dm_exec_” for execution-related objects, “dm_os_” for SQL Operating System (SQLOS) objects, and many more.
Let’s explore a practical example of how DMOs can be used. One common scenario is when a connection is causing resource blocking and slowing down the system. In previous versions of SQL Server, you would need to have a trace running in Profiler to capture the blocking statement. However, starting from SQL Server 2005, you can leverage DMOs to get real-time insights into the executing query.
Here’s a step-by-step example:
- Create a stored procedure that starts a transaction, updates all rows in a table, and then waits for an hour.
- Execute the stored procedure and note the session ID of the query window where it is executed.
- Use the session ID to query the dynamic management view sys.dm_exec_requests, which provides information about the currently executing requests. Look for the columns “sql_handle” and “plan_handle”, which are hash values representing the SQL text and execution plan of the request.
- Use the dynamic management function sys.dm_exec_sql_text to retrieve the actual SQL statement(s) corresponding to the hash value obtained in the previous step.
- To further analyze the query, pass the plan_handle to the dynamic management function sys.dm_exec_query_plan, which returns the query plan in the showplan XML format. This XML can be viewed in SQL Server Management Studio or saved as a .sqlplan file for graphical representation.
By leveraging DMOs, you can gain valuable insights into the current state of SQL Server and identify performance bottlenecks more effectively. These objects are essential tools for performance tuning and troubleshooting.
It’s important to note that this article only scratches the surface of what DMOs can do. There are many more dynamic views and functions available for exploring different aspects of SQL Server.
Give DMOs a try and unlock the power of SQL Server’s inner workings!