Increased CPU usages during SQL manged instance Maintenance

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Increased CPU usages during SQL manged instance Maintenance

Joby Mathew 5

One of our SQL Managed Instances experienced a CPU usage increase from 40% to 90%, despite a constant user workload. We noticed that SQL was restarted around time, and Azure has confirmed ongoing maintenance through notification. However, the maintenance notification only mentioned a possible drop in connectivity, not a rise in CPU usage. Could you please advise?

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Answer 1

Erland Sommarskog 121.3K MVP Volunteer Moderator

If SQL Server is restarted the plan cache goes out the window, so all queries has to be compiled anew. Likewise the buffer cache also goes away, so data has to be read from disk. So, yes, it is a expected to see a temporary increase of CPU after a server restart.

If the CPU remains on a high level, that suggest that some of the query plans are not the same as before, and some of them are less appropriate. If you find the Query Store for the database in Management Studio, the node Regressed Queries may reveal the culprit(s).

Joby Mathew 5 Reputation points

2025-06-14T19:21:47.9+00:00

Thanks for the comments!

I don’t believe the issue is related to caching, as a temporary CPU spike is expected after a service restart. However, in this case, the high CPU usage persisted for an extended period—over 10 hours. Eventually, we decided to restart the service, which brought the CPU usage down from 80–90% to 30–40%. So I suspect something in the underlying infrastructure may have been affected by the recent Azure scheduled maintenance

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Increased CPU usages during SQL manged instance Maintenance

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