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From: Francois Richard <frichard@xobni.com>
To: "user@cassandra.apache.org" <user@cassandra.apache.org>,
	"cassandra-user@incubator.apache.org" <cassandra-user@incubator.apache.org>
Date: Sat, 23 Jul 2011 17:16:37 -0400
Thread-Topic: do I need to add more nodes? minor compaction eat all IO
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Subject: RE: do I need to add more nodes? minor compaction eat all IO

This really depends on your disks setup.

When you run iostat under high load, do you see a high number of r/s but th=
e rMB/s is not so great?

I usually use:

iostat -x -m sdb sdc 1 to monitor situation like this.


In my case my disk setup is the following:

OS --> /sda
Cassandra CommitLogs --> /sdb
Cassandra Data --> /sdc

My understanding is that during compaction cassandra does a lot of non sequ=
ential readsa then dumps the results with a big sequential write.

Is your application mostly doing writes and little reads or the other way a=
round.


FR

-----Original Message-----
From: Yan Chunlu [mailto:springrider@gmail.com]=20
Sent: Saturday, July 23, 2011 9:16 AM
To: cassandra-user@incubator.apache.org
Subject: do I need to add more nodes? minor compaction eat all IO

I have three nodes and RF=3D3, every time it is do minor compaction, the cp=
u load(8 core) get to >30, and iostat -x 2 shows utils is 100%, is that mea=
ns I need more nodes?  the total data size is <60G

thanks!

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