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From Marcin Pietraszek <mpietras...@opera.com>
Subject High CPU load
Date Mon, 20 Jul 2015 07:15:44 GMT
Hello!

I've noticed a strange CPU utilisation patterns on machines in our
cluster. After C* daemon restart it behaves in a normal way, after a
few weeks since a restart CPU usage starts to raise. Currently on one
of the nodes (screenshots attached) cpu load is ~4. Shortly before
restart load raises to ~15 (our cassandra machines have 16 cpus).

In that cluster we're using bulkloading from hadoop cluster with 1400
reducers (200 parallel bulkloading tasks). After such session of heavy
bulkloading number of pending compactions is quite high but it's able
to clear them before next "bulkloading session". We're also tracking
number of pending compactions and during most of the time it's 0.

On our machines we do have a few gigs of free memory ~7GB (17GB used),
also it seems like we aren't IO bound.

Screenshots from our zabbix with CPU utilisation graphs:

http://i60.tinypic.com/xas8q8.jpg
http://i58.tinypic.com/24pifcy.jpg

Do you guys know what could be causing such high load?

-- 
mp

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