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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Update of "DigestQueries" by PeterSchuller
Date Tue, 12 Apr 2011 22:26:02 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Cassandra Wiki" for change notification.

The "DigestQueries" page has been changed by PeterSchuller.
http://wiki.apache.org/cassandra/DigestQueries

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New page:
A "digest" query is like a ready query except that instead of the receiving node actually
returning the data, it only returns a digest (hash) of the would-be data.

The intent of submitting a digest query is to discover whether two or more nodes agree on
what the current data is, without sending the data over the network. In particular for large
amounts of data, this is a significant saving of bandwidth cost relative to sending the full
data response.

Keep in mind that the cost of potentially going down to disk, and most or all of the CPU cost,
associated with a query will still be taken on nodes that receive digest queries. The optimization
is only for bandwidth.

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