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From Reik Schatz <>
Subject write count increase after 1.2 update
Date Tue, 15 Jan 2013 17:23:53 GMT
Hi, we are running a 1.1.6 (datastax) test cluster with 6 nodes. After the
recent 1.2 release we have set up a second cluster - also having 6 nodes
running 1.2 (datastax).

They are now running in parallel. We noticed an increase in the number of
writes in our monitoring tool (Datadog). The tool is using the write count
statistic of nodetool cfstats. So we ran nodetool cfstats on one node in
each cluster. To get an initial write count. Then we ran it again after 60
sec. It looks like the 1.2 received about twice the amount of writes.

The way our application is designed is that the writes are idempotent, so
we don't see a size increase. Were there any changes in between 1.1.6 > 1.2
that could explain this behavior?

I know that 1.2 has the concept of virtual nodes, to spread out the data
more evenly. So if the "write count" value was actually the sum of all
writes to all nodes in the, this increase would make sense.


ps. the clusters are not 100% identical. i.e. since bloom filters are now
off-heap, we changed settings for heap size and memtables. Cluster 1.1.6:
heap 8G, memtables 1/3 of heap. Cluster 1.2.0: heap 4G, memtables 2G. Not
sure it can have an impact on the problem.

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