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Adam Machanic

Adam Machanic, Boston-based SQL Server developer, shares his experiences with programming, monitoring, and performance tuning SQL Server. And the occasional battle with the query optimizer.

Delta Force (A Month of Activity Monitoring, Part 26 of 30)


Published Tuesday, April 26, 2011 11:00 AM by Adam Machanic



Igor Marchenko said:


   First of all kudos for your series! I learned a lot about powerful functionality of sp_WhoISActive. I used to sample CPU, reads, writes per interval manually (I had a script for that). sp_WhoISActive will certainly be a replacement for homegrown script I used.

Thanks again,


April 28, 2011 5:23 PM

Adam Machanic said:

This post is part 28 of a 30-part series about the Who is Active stored procedure. A new post will run

April 28, 2011 9:03 PM

Adam Machanic said:

This post is part 30 of a 30-part series about the Who is Active stored procedure. A new post will run

April 30, 2011 11:45 AM

Ethan Murray said:

I've been looking for something like delta_mode for months.  I run big reporting-centric databases full of long-running ad hoc queries, and I often need to get in and see why CPU is running hot, and who wrote the bad query.  Nothing else I've tried has been so convenient and useful.

September 8, 2012 7:02 AM

Paulo said:

Delta mode & output to table.  Bingo!

November 2, 2015 11:33 PM

Praveen said:

Hi Adam,

What does it mean if CPU_Delta is NULL? I am getting records with CPU_Delta as NULL.


November 2, 2016 6:02 AM

Adam Machanic said:


Delta mode does two collections. First it does a base collection ("X"), then a delta collection ("Y"). All requests/sessions that exist as of "Y" will be output, but delta metrics can only be calculated for rows that are also in "X." So in your case, you had some new sessions/requests start after the base collection, and the proc doesn't have enough information to calculate a delta so it sends back NULL.

Make sense?


November 2, 2016 10:16 AM

Praveen said:

Thanks for the quick response.

November 2, 2016 11:28 AM
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About Adam Machanic

Adam Machanic is a Boston-based SQL Server developer, writer, and speaker. He focuses on large-scale data warehouse performance and development, and is author of the award-winning SQL Server monitoring stored procedure, sp_WhoIsActive. Adam has written for numerous web sites and magazines, including SQLblog, Simple Talk, Search SQL Server, SQL Server Professional, CoDe, and VSJ. He has also contributed to several books on SQL Server, including "SQL Server 2008 Internals" (Microsoft Press, 2009) and "Expert SQL Server 2005 Development" (Apress, 2007). Adam regularly speaks at conferences and training events on a variety of SQL Server topics. He is a Microsoft Most Valuable Professional (MVP) for SQL Server, a Microsoft Certified IT Professional (MCITP), and an alumnus of the INETA North American Speakers Bureau.

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