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[Question #226895]: carbon-cache IO reads problem

To: graphite-dev@xxxxxxxxxxxxxxxxxxx
From: kaarel <question226895@xxxxxxxxxxxxxxxxxxxxx>
Date: Wed, 17 Apr 2013 10:46:05 -0000
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New question #226895 on Graphite:
https://answers.launchpad.net/graphite/+question/226895

I had a problem where carbon-cache was generating a lot of IO reads even though no graphs were being made.

Setup Linux VM with 2G memory
~150 000 metrics with 30 000 updates coming in every minute

When update count climbed from 15k to 30k I started noticing a lot of IO reads (basically same amount as writes).
The problem is that each write also does some minor reads inside the file (metadata and aggregation). If those files cannot fit inside kernel page cache then it will start hitting disc.

So when noticing a lot of IO reads - you probably have to add more RAM to the machine/VM to solve the problem.

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