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From Peter Tillotson <>
Subject Re: performance reaching plateau while the hardware is still idle
Date Thu, 15 Dec 2011 17:45:03 GMT
May I suggest dstat, does cpu, memory, and io on one console
dstat -vn 3

So possible causes
 * Not sufficient parrallelism in the client
 * Server has too few threads
 * You are not CPU bound, network or disk may be the bottleneck 


----- Original Message -----
From: Kent Tong <>
To: "" <>
Sent: Thursday, 15 December 2011, 10:58
Subject: performance reaching plateau while the hardware is still idle


I am running a performance test for Cassandra 1.0.5. It can perform about 1500 business operation
(one read+one write to the same row) per second. However, the CPU is still 85% idle (as shown
by vmstat) and the IO utilization is less than a few percent (as shown by iostat). "nodetool
tpstats" shows basically no active and pending threads. I can run several such test clients
concurrently, achieving the same operations per second without increasing the hardware utilization.
So, why the performance has reached a plateau while there is still idle hardware resources?

Thanks in advance for any idea!

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