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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-192) Load balancing
Date Tue, 26 May 2009 15:38:45 GMT


Jonathan Ellis commented on CASSANDRA-192:

The Rao paper (or RLS+03, as it is cited in the other) describes three schemes to balance
the load among machines by giving each several "virtual nodes" (as in Dynamo) and moving or
splitting nodes from heavily loaded machines to lightly loaded.  A scheme like this is relatively
simple once you already have a virtual node system in place but we do not and we would prefer
not to add that layer of complexity if we can avoid it.

> Load balancing
> --------------
>                 Key: CASSANDRA-192
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: Jonathan Ellis
>             Fix For: 0.4
> We need to be able to spread load evenly across a cluster to mitigate keys not being
uniformly distributed as well as heterogeneous nodes in a cluster.  The former is particularly
likely to be a problem when using the OrderPreservingPartitioner, since the keys are not randomized
by a hash function.
> Avinash suggested three papers on load balancing in this thread:
> Of these, the useful ones are
> (Simple Efficient Load Balancing
Algorithms for Peer-to-Peer Systems by David R. Karger and Matthias Ruhl)
> (Load Balancing in Structured
P2P Systems by Ananth Rao et al)
> The third, 
> (Simple Load Balancing
for Distributed Hash Tables by John Byers et al) is not applicable to Cassandra's design.
 ("First, we suggest the direct application of the 'power of two choices' paradigm, whereby
an item is stored at the less loaded of two (or more) random alternatives. We then consider
how associating a small constant number of hash values with a key can naturally be extended
to support other load balancing strategies.")

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