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[chrismd <question80372@xxxxxxxxxxxxxxxxxxxxx>]

Question #80372 on Graphite changed:
https://answers.launchpad.net/graphite/+question/80372

    Status: Open => Answered

chrismd proposed the following answer:
Yes you can do this with the offset() function (grab the latest trunk
code).

For (100 - instance.cpu_idle) / 100 you would do something like this:

target=scale(offset(scale(instance.cpu_idle,-1),100),0.01)

The result would be a series whose values range from 0.0 to 1.0
indicating the percentage of non-idle cpu.

As for multiplying two series there is not currently a function
implemented that supports this but it would be pretty easy to do. Look
in $GRAPHITE_ROOT/webapp/web/render/functions.py if your are interested.

One thing I would note about your example of calculating capacity. This
would only be accurate if there is a linear relationship between cpu use
and requests per second (which may not be possible to assert if you have
more than one instance per machine & uneven load balancing, or multi-
core machines & a threaded application, etc...). Then again, it may turn
out that it works fine in practice. Plus it might still be a useful
metric even if it does not exactly represent remaining capacity in
requests per second. It is definitely an interesting idea.

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