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I have a physical server running one instance of SQL Server.

I notice that quite often this server is running at 100% CPU usage.

My IT team is not happy about this, and suggested we reserve 2 of the 32 cores for the OS.

This works great, now max usage peak just under 90%. Additionally, slow data retrieval from various users is no longer reported.

Is there any reason NOT to use WSRM (Windows System Resource Manager) in this way - instead of SQL Resource Governor?

  • Do you really want to use all the CPU? Saving a couple of cores for the OS seems prudent doesn't it? On my workstation, if I use all cores for some number crunching my machine grinds to a halt. I always keep a few cores free. Would this not be good practice on a machine dedicated to SQL Server too? – ManInMoon Mar 20 at 12:22
  • What kind of load is running on this server? What type of process is using 100% of CPU? Is this OLTP or analytics or graph or ? – Max Vernon Mar 20 at 12:40
  • @Forrest When you say tuning - do you mean the SQL Server itself - or the queries/table structure? If you mean SQL Server, please give me a link to what to look at. If queiries/tables, then I optmise them when I can, but some users are less design conscious! – ManInMoon Mar 20 at 12:45
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Is there any reason NOT to use the approach you've defined? Absolutely.

Imagine you had bought a car - a car that when you hit 50MPH the engine starts to overheat. Would your reaction to this situation be to artificially limit the car to 49MPH, or to find out what the fault is with the engine?

Why should you limit your car to 49MPH? The manufacturer stated that it could drive as fast as 80MPH - you like to drive your car fast so you want to get it to this speed - if it wasn't for that damn overheating issue.

The car you bought was also really, really expensive. Each engine cylinder needs to be utilised to the max so you aren't wasting that money!

By artificially limiting SQL Servers access to the CPU, you are missing out on performance. You may have temporarily resolved the performance issues by ensuring the CPU is available for the OS to use, but you haven't answered the real question - WHY is SQL Server using 100% of the CPU?

My advice is as follows:

Find out what the real issue is, and fix it. Don't cover the issue up with what is effectively a kludge. The issue WILL reappear and smack you in the face down the line when the workload of the server naturally increases with growth.

As a temporary fix, resource governor can be used to lower the CPU used, UNTIL YOU FIND THE REAL PROBLEM.

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Erik Darling mentioned the biggest practical reason for not using WSRM in a comment on your question:

...there's no reciprocal limiting of CPU use in other processes. SQL Server may not use those two cores, but other things may use the other 30 SQL Server is using. It's a crapshoot, really.

If this is working for you, then stick with it - we're all busy, and you can only spend so much time on any given problem. The ideal solution would be to fix the underlying queries / issues that are driving CPU to the point of user-noticeable problems (which George covers in his excellent answer).

Erik goes on to say

Plus, you're paying SQL Server licensing for them.

From a business standpoint, this is probably the worst part of the WSRM deal - you're paying per-core licensing for 2 cores that are explicitly not being used. At the time of this writing, that's $3k or $14k left on the table (depending on Standard vs Enterprise).

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