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From Markus Klems <>
Subject Benchmarking Cassandra with YCSB
Date Tue, 15 Feb 2011 19:45:29 GMT
Hi there,

we are currently benchmarking a Cassandra 0.6.5 cluster with 3
High-Mem Quadruple Extra Large EC2 nodes
( using Yahoo's YCSB tool
(replication factor is 3, random partitioner). We assigned 32 GB RAM
to the JVM and left 32 GB RAM for the Ubuntu Linux filesystem buffer.
We also set the user count to a very large number via ulimit -u

Our goal is to achieve max throughput by increasing YCSB's threadcount
parameter (i.e. the number of parallel benchmarking client threads).
However, this does only improve Cassandra throughput for low numbers
of threads. If we move to higher threadcounts, throughput does not
increase and even  decreases. Do you have any idea why this is
happening and possibly suggestions how to scale throughput to much
higher numbers? Why is throughput hitting a wall, anyways? And where
does the latency/throughput tradeoff come from?

Here is our YCSB configuration:
threadcount= 500
target = 10000

These are typical results for threadcount=1:
Loading workload...
Starting test.
 0 sec: 0 operations;
 10 sec: 11733 operations; 1168.28 current ops/sec; [UPDATE
AverageLatency(ms)=0.64] [READ AverageLatency(ms)=1.03]
 20 sec: 24246 operations; 1251.68 current ops/sec; [UPDATE
AverageLatency(ms)=0.48] [READ AverageLatency(ms)=1.11]

These are typical results for threadcount=10:
10 sec: 30428 operations; 3029.77 current ops/sec; [UPDATE
AverageLatency(ms)=2.11] [READ AverageLatency(ms)=4.32]
 20 sec: 60838 operations; 3041.91 current ops/sec; [UPDATE
AverageLatency(ms)=2.15] [READ AverageLatency(ms)=4.37]

These are typical results for threadcount=100:
10 sec: 29070 operations; 2895.42 current ops/sec; [UPDATE
AverageLatency(ms)=20.53] [READ AverageLatency(ms)=44.91]
 20 sec: 53621 operations; 2455.84 current ops/sec; [UPDATE
AverageLatency(ms)=23.11] [READ AverageLatency(ms)=55.39]

These are typical results for threadcount=500:
10 sec: 30655 operations; 3053.59 current ops/sec; [UPDATE
AverageLatency(ms)=72.71] [READ AverageLatency(ms)=187.19]
 20 sec: 68846 operations; 3814.14 current ops/sec; [UPDATE
AverageLatency(ms)=65.36] [READ AverageLatency(ms)=191.75]

We never measured more than ~6000 ops/sec. Are there ways to tune
Cassandra that we are not aware of? We made some modification to the
Cassandra 0.6.5 core for experimental reasons, so it's not easy to
switch to 0.7x or 0.8x. However, if this might solve the scaling
issues, we might consider to port our modifications to a newer
Cassandra version...


Markus Klems

Karlsruhe Institute of Technology, Germany

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