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From David Jeske <>
Subject Re: cassandra vs hbase summary (was facebook messaging)
Date Mon, 22 Nov 2010 20:05:29 GMT
> 2) Cassandra has a less efficient memory footprint data pinned in
> memory (or cached). With 3 replicas on Cassandra, each element of data
> pinned in-memory is kept in memory on 3 servers, wheras in hbase only
> region masters keep the data in memory, so there is only one-copy of
> each data element.
> True in the general case, but if you want to optimize for READ.ONE. We
> can make our caches work like hbase.

Forgive my limited understanding of Cassandra, but I don't understand that
issue commentary. Can you clarify?

"snitch that prefers a single replica for all reads to a given key" sounds
like 1/2 of  "electing a master for a row range". However, the other half is
assuring that all writes must include this replica. Otherwise if you did
N3/W2/R1, you might write to the two copies that were not the "single
preferred replica master".  Did I understand that correctly?

> #4 Not a fair comparison. If hbase is happy working with 2/3 replicas
> it is not equal to Write.ALL Read.ONE.

Agreed. The reason I included it is that people discuss both N3/W2/R2 and
N3/W3/R1 as possible matches for hbase functionality. They refer to N3/W3/R1
because it allows reads to come from a single server, just like in hbase.

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