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From Katriel Traum <katr...@google.com>
Subject Impact of adding nodes to cluster
Date Thu, 24 Apr 2014 13:21:30 GMT
Hello list,

I have a cluster of 3 nodes with RF=3. The cluster load is daily bulk
write/delete/compact, and read the rest of the time.
For better read performance, and to make sure data is 100% consistent, we
write with "ALL" and read "ONE", stopping the write process if there is a
problem.

My problem is that I've maxed out my network cards. I do not have separate
cards for inter-node communication.
The knee jerk reaction was adding more nodes, but I'm not sure what
replication factor to set, 3 or 6.
My first thought was to leave it at 3, but having 6 nodes, means that if
the co-ordinator does not have the data, it will read it from another node:
1. Data Node -> Coordinator
2. Coordinator -> Client
This effectively means that I double the amount of data going through the
system:

Setting it to RF=6, means that every node will always have a replica of the
data, and reading with "ONE", will always be contained in the co-ordinator.
The downside is I loose the added value of redundancy during the write
cycle.

Does anyone have an insight or idea if my assumptions are correct? Does
inter-node communication really add all this network overhead?

Thanks,
Katriel

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