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From jmodha <>
Subject Seeing writes when only expecting reads
Date Thu, 19 Jul 2012 17:17:14 GMT

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

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