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Caching and Replication: The Differences

As always a fantastic read from Jeff Darcy:

A replica is supposed to be complete and authoritative. A cache can be incomplete and/or non-authoritative.

I’m using “suppose” here in the almost old-fashioned sense of assume or believe, not demand or require. The assumption or belief might not actually reflect reality. A cache might in fact be complete, while a replica might be incomplete – and probably will be, when factors such as propagation delays and conflict resolution are considered. The important thing is how these two contrary suppositions guide behavior when a client requests data. This distinction is most important in the negative case: if you can’t find a datum in a replica then you proceed as if it doesn’t exist anywhere, but if you can’t find a datum in a cache then you look somewhere else. Here are several other possible distinctions that I think do not work as well.

Original title and link: Caching and Replication: The Differences (NoSQL databases © myNoSQL)

via: http://pl.atyp.us/wordpress/?p=3149