PREEMPTIVE_OS_GETPROCADDRESS is a new wait type that was introduced in SQL Server 2008 to track time taken by GetProcAddress to load the entrypoint in the DLL when Extended Stored Procedure calls are made by the SQL Server instance. However, the way the wait time is tracked by this wait type has a little quirk which Rob Dorr had documented in a blog post.
Based on a discussion on #sqlhelp thread on Twitter, I found the need to demonstrate this unique quirk with the help of an example. I am using the following command to list you the sub-directories on my C: drive using the command:
exec master..xp_dirtree ‘C:\’
Next I monitored the wait statistics for the session executing this Extended Stored procedure using the T-SQL script below with a 1 second delay:
SET NOCOUNT ON WHILE (1=1) BEGIN SELECT [session_id], [status], [command], [start_time], [cpu_time], [reads], [writes], [wait_resource], [wait_time], [last_wait_type], [wait_type] FROM sys.dm_exec_requests WHERE [session_id] = 53 -- Session ID that is executing the Extended Stored Procedure WAITFOR DELAY '00:00:01' RAISERROR ('', 10, 1, N'Waits'); END
The output of this script was as follows:
session_id status command start_time cpu_time reads writes wait_time last_wait_type wait_type
53 runnable EXECUTE 2011-07-20 00:59:44.330 62 0 0 712 PREEMPTIVE_OS_GETPROCADDRESS PREEMPTIVE_OS_GETPROCADDRESS
53 running EXECUTE 2011-07-20 00:59:44.330 234 0 0 1713 PREEMPTIVE_OS_GETPROCADDRESS PREEMPTIVE_OS_GETPROCADDRESS
53 runnable EXECUTE 2011-07-20 00:59:44.330 452 0 0 2714 PREEMPTIVE_OS_GETPROCADDRESS PREEMPTIVE_OS_GETPROCADDRESS
As you can see above the wait time keeps increasing even though I can see that the session is performing work due to the following results:
a. The results window in SSMS for the session executing the extended stored procedure was churning out results
b. Using a Process Monitor, I could trace the filesystem activity on the C: drive for the SQL Server process
You could run into this issue while using any Extended Stored Procedure (system or user) for a SQL Server 2008 or SQL Server 2008 R2 instance. Since I know that the session is performing work, the only two other things that I would check if there are resource bottlenecks w.r.t. memory or I/O if some filesystem related activity is being performed by the extended stored procedure. Most of the issues where I have see this wait type causing confusion is when the extended stored procedure is performing disk related activity. At that time, Process Monitor will put your doubts to rest along with the information that I mentioned above to confirm that that the procedure is actually doing some work and not stuck or perceived as “hung”.