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[Sidnei da Silva <question212303@xxxxxxxxxxxxxxxxxxxxx>]

Question #212303 on Graphite changed:
https://answers.launchpad.net/graphite/+question/212303

    Status: Open => Answered

Sidnei da Silva proposed the following answer:
Setting MAX_UPDATES_PER_SECOND (3) should do the trick.

You can find the optimal number by dividing 1/avgUpdateTime/number of
carbon-cache processes and shooting for a little under that. Once you
restrict the number of writes, carbon-cache will naturally queue up
writes (which is (2) above).

As an example, I have an installation handling 70000 metrics.
avgUpdateTime was hovering around 0.005 with MAX_UPDATES_PER_SECOND 400
and IO utilization was 100% consistently. This had 6 carbon-cache
processes.

So: 1/0.005/6 = 33.333333333333336. I've set MAX_UPDATES_PER_SECOND = 30
for each carbon-cache and now IO is consistently below 10% with
pointsPerUpdate hovering around 8. I could raise that a little bit to
get pointsPerUpdate to 4-5, but haven't bothered so far.

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