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  • Writer's pictureJeff Taylor

Max Degree of Parallelism - Does it Matter?

Recently I encountered a Microsoft SQL Server with relatively high and very consistent CPU usage with few peaks and valleys.

When checking the server CPU configuration, I noticed that the server had 10 virtual CPUs.


When I checked the SQL Server configuration, the server was only using a max of 4 for parallel processing.




Next, I looked to see if the server had NUMA nodes and how many processors were in each NUMA node.


To find out how many NUMA nodes your server or VM might have, open up task manager, go to the CPU tab, right mouse click, select 'change graph to', then select 'NUMA nodes'.



Next, I looked to see if the server had NUMA nodes and how many processors were in each NUMA node.



To find out how many NUMA nodes your server or VM might have, open up task manager, go to the CPU tab, right mouse click, select 'change graph to', then select 'NUMA nodes'.



Immediately you could see the overall server CPU usage drop.



You can see here that the transactions now have peaks and valleys.



I also noticed another change to Disk IO. The server was able to start working, which required more IO.

The server was actually able to do more work and pull more data from the SAN. Here is what that looked like.


In conclusion, does Max Degree of Parallelism and NUMA node matter? Yes!

(The monitoring tool used to monitor this server was Sentry One's SQL Sentry)

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