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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Location-aware replication based on objects' access pattern
Date Wed, 06 Apr 2011 01:59:01 GMT
On Tue, Apr 5, 2011 at 8:37 PM, Yudong Gao <stgyd@umich.edu> wrote:
> One thing I am worrying about is how to maintain the location
> information for each row. The current partitioner maps a key to MD5
> hash, and it is almost impossible to control the hashed token by
> manipulating the value of the key. Also, maintaining a key-to-location
> mapping would be unscalable. My initial thought is to use the key
> string as the token directly, so that the location information can be
> binded into the key. This minimize the changes to the other
> components.

This is what ByteOrderedPartitioner does, but that tends to create hot
spots since sequential keys are stored on the same node.

A better solution would be to just push the DecoratedKey into the
ReplicationStrategy so it can make its decision before information is
thrown away.

> Do you know how the existing application is achieving this without the
> per-row support?

All existing applications places replicas by keyspace, not by row.

-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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