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From Ikeda Anthony <>
Subject Re: Local Quorum Performance...
Date Sat, 17 Sep 2011 19:15:46 GMT
What snitch do you have configured? We typically see a proper spread of data across all our
nodes equally.


On 17/09/2011, at 10:06 AM, Chris Marino wrote:

> Hi, I have a question about what to expect when running a cluster across datacenters
with Local Quorum consistency.
> My simplistic assumption is that the performance of an 8 node cluster split across 2
data centers and running with local quorum would perform roughly the same as a 4 node cluster
in one data center.
> I'm 95% certain we've set up the keyspace so that the entire range is in one datacenter
and the client is local. I see the keyspace split across all the local nodes, with remote
nodes owning 0%. Yet when I run the stress tests against this configuration with local quorum,
I see dramatically different results from when I ran the same tests against a 4 node cluster.
 I'm still 5% unsure of this because the documentation on how to configure this is pretty
> My understanding of Local Quorum was that once the data was written to a local quorum,
the commit would complete. I also believed that this would eliminate any WAN latency required
for replication to the other DC.
> It not just that the split cluster runs slower, its also that there is enormous variability
in identical tests. Sometimes by a factor of 2 or more. It seems as though the WAN latency
is not only impacting performance, but that it's also introducing a wide variation on overally
> Should WAN latency be completely hidden with local quorum? Or are there second order
issues involved that will impact performance??
> I'm running in EC2 across us-east/west regions. I already know how unpredictable EC2
performance can be, but what I'm seeing with here is far beyond normal.performance variability
for EC2
> Is there something obvious that I'm missing that would explain why the results are so
> Here's the config when we run a 2x2 cluster:
> Address         DC          Rack        Status State   Load            Owns    Token
>                                                                                85070591730234615865843651857942052865
>     us-east     1b          Up     Normal  25.26 MB        50.00%  0    
>     us-west     1c          Up     Normal  12.68 MB        0.00%   1    
>     us-east     1b          Up     Normal  12.56 MB        50.00%  85070591730234615865843651857942052864
>     us-west     1c          Up     Normal  25.48 MB        0.00%   85070591730234615865843651857942052865
> Thanks in advance.
> CM

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