By: Tim Ford | Last Updated: 2009-07-22 | Comments (2) | Dynamic Management Views and Functions
I was reading a recent blog post from Pinal Dave, SQL Server MVP, regarding returning information on the latest query executed for a given session. He offered up a couple options to return the last query statement executed, settling upon querying the sys.sysprocesses system compatibility view, but another way that this can be done is through the Dynamic Management Views and Functions. The process for doing so is quite straight-forward and works in all versions of Microsoft SQL Server since DMOs (dynamic management objects) were integrated into SQL Server.
Before proceeding we should take a second to explain what a session is. In Microsoft SQL Server, a session is synonymous with a user process. Previous to SQL 2005 sessions were referred to - and identified solely - as SPIDs (short for session id). A SPID uniquely identifies a session and a SPID is unique across the SQL Server instance. In an attempt to conform SQL Server object identifiers to be more user-friendly and to standardize a naming convention across all system objects, sessions are now identified across the DMO and system catalog views as session_id. You'll see similar changes between previous versions of SQL Server and current versions where all object identifiers are concerned.
You can use the @@spid() system function to return the session_id of the current session as follows:
For my test I get session_id = 52.
So, now that we've identified what session_id uniquely identifies the session I'm using during this demonstration, I'll do a simple query against the Northwind database.
At this point I'll now open up a separate query window in SQL Server Management Studio. If I now execute the first query above you'll see that this registers as a new session on the SQL Server instance:
For my test I get session_id = 53
Now I can utilize the sys.dm_exec_connections Dynamic Management View, in conjunction with the sys.dm_exec_sql_text Dynamic Management Function to return the last query statement executed against the SQL Server instance on a selected session. In all truth, you can return the last query executed on all sessions, but for the sake of this discussion we're limiting the results based upon the session_id (52) we've identified above. I'll present the query, then we can examine in detail what it provides for us.
The output for this query shows the statement that was run for session_id 52.
So what just happened? Simply-put, we returned the results from the sys.dm_exec_connections DMV, limiting the results by the session_id (52) we identified above. We, submitted the value contained in the most_recent_sql_handle column of this DMV to the sys.dm_exec_sql_text Dynamic Management Function. That function then returned as text, the value of the sql_handle we passed to it.
So what is a sql_handle? Think of a sql_handle as a unique identifier for a query that is unique across the entire SQL Server instance. Just as a session_id uniquely identifies a session, so does a sql_handle identify a query. The actual value of the sql_handle column is very cryptic. The value for the most_recent_sql_handle in this example is shown below:
Here we can see the value of the sql_handle and the text translation.
The handle itself does not really do much for us without the function call that rationalizes it into the original query text. As you can see though, this very simple query does provide us with yet another option for returning information on what users are (or have been) doing on the SQL Server instances we support.
- The Dynamic Management Objects have so much to offer the DBA. Check out other tips on DMOs from MSSQLTips.com.
- Read more tips by the author here.
- Still interested in information on sysprocesses, whether as a system table (pre-SQL 2005) or system view? Here are some tips that meet your needs.
Last Updated: 2009-07-22
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