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We have a SQL Server which suddenly started running at 98%-100% CPU. No idea why. When we turn on SQL Server Profiler, it drops to the 70% range.

Any ideas?

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up vote 5 down vote accepted

I suspect you're seeing lower CPU utilization because the SQL Server Profiler is introducing latency. You should find that your problematic queries run even slower when the Profiler is running.

CPU usage notwithstanding the Profile is going to show you what's really going on.

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Long shot - if the server is a virtual machine, or has power-saving CPUs, perhaps the 98-100% is not the true full CPU capacity. By giving extra demand, perhaps more CPU capacity kicks in?

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