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From aaron morton <aa...@thelastpickle.com>
Subject Re: Seeing writes when only expecting reads
Date Fri, 20 Jul 2012 09:21:03 GMT
My first guess would be read repair, are you seeing any increase in ReadRepairStage tasks ?


RR (in 1.X) is normally only enabled for 10% of the request.

cheers

-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 20/07/2012, at 5:17 AM, jmodha wrote:

> Hi,
> 
> We've observed a some strange behaviour after finishing streaming data into
> our new cluster.
> 
> Below are the steps we're doing:
> 
> 1 - We stream data from an old cluster (1.0.3) to a new cluster (1.1.1).
> This completes with no errors.
> 2 - We then run some validation scripts (some Java code which uses hector)
> to ensure what we've streamed in matches the data in our old cluster.
> 3 - The validation script is a read-only operation, but when observing the
> WriteCount JMX property on one of the column families its continuously
> increasing across all nodes!
> 
> I have verified that we only do reads and no writes, so why am I seeing the
> WriteCount JMX property increasing on all of my nodes for this one column
> family only?
> 
> Some other info.. we're reading at LOCAL_QUORUM, its a two DC setup, 6 nodes
> in each DC. All of our CF's have rows that contain a mixture of TTL and
> non-TTL columns.
> 
> Any ideas as to why this is happening would be greatly appreciated!
> 
> P.S. I've attached some graphs which show reads vs. writes on the CF in
> question.
> 
> http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/file/n7581333/reads.png

> http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/file/n7581333/writes.png

> 
> --
> View this message in context: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Seeing-writes-when-only-expecting-reads-tp7581333.html
> Sent from the cassandra-user@incubator.apache.org mailing list archive at Nabble.com.


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