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From Jérémy SEVELLEC <jsevel...@gmail.com>
Subject Re: weird problem with performance
Date Wed, 19 Oct 2011 21:10:15 GMT
Ok.

I think a degration could be normal because your cluster is in a degraded
state when a node is down.

With a replication_factor of 3 and with a 3 nodes cluster, each data you
write is replicated on each node. As One node is down, when writing, it's
impossible to send a replica on the down node and hints are send :
http://www.datastax.com/docs/1.0/dml/about_writes#hinted-handoff-writes
And it could be more expensive to achieve QUORUM when you read in that
context.

It may be one explanation. You can turn cassandra log into debug level to
see what happen when when there is a down node.

2011/10/19 Yang <teddyyyy123@gmail.com>

> 3
>
> sorry forgot this important info
> On Oct 19, 2011 11:31 AM, "Jérémy SEVELLEC" <jsevellec@gmail.com> wrote:
>
>> Hi, what is your replication_factor?
>>
>> 2011/10/19 Yang <teddyyyy123@gmail.com>
>>
>>> I'm using a cassandra version compiled from 1.0.0  github HEAD.
>>>
>>> I have 3 nodes, A B and C,  on node A I run a client, which talks only
>>> to B as the coordinator.
>>>
>>> the performance is pretty good, a QUORUM read+write  takes < 10ms.
>>>
>>> but then I shutdown C, quickly the performance starts to degrade, and
>>> QUORUM read+write time steadily increase to about 300ms.
>>>
>>> if I shutdown A and keep C, I observe the same effect.
>>>
>>>
>>> I understand that "2 out of 3" is going to give you faster response
>>> than "2 out of 2", but  the difference should not be that dramatic as
>>> 10ms vs 300ms.
>>>
>>> any possible reasons for this?(or how to debug this?)
>>>
>>> Thanks
>>> Yang
>>>
>>
>>
>>
>> --
>> Jérémy
>>
>


-- 
Jérémy

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