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What are the operating system overheads of running dtrace?

That is sort of a loaded question, but we have a nice general answer for it - The probe-effect of DTrace is proportional to the question you ask.

What that means is that if you enable specific probes to concisely answer a question, the probe-effect of DTrace will be almost immeasurable. For instance, you would be adding less than a few microseconds to an I/O request if you were to use the io provider to look at disk access. For a millisecond operation, this would not be a big deal.

Now, if you enable the thousands of probes - to say, instrument every function in Oracle - the probe-effect would be quite high.

The key is to use formulate your question (DTrace script) in the most specific way to get a concise answer.

That being said, I have instrumented every single kernel function and still had a quite usable system (though not recommended in production).

Thanks,

Jarod