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From Jonathan Ellis <>
Subject Re: Effective cache size
Date Thu, 03 Jun 2010 06:32:05 GMT
On Wed, Jun 2, 2010 at 10:39 PM, David King <> wrote:
> If I go to fetch some row given the rack-unaware placement strategy, the default snitch
and CL==ONE, the node that is asked is the first node in the ring with the datum that is currently
up, then a checksum is sent to the replicas to trigger read repair as appropriate.


> So with the row cache, that first node (the primary replica) is the one that has that
row cached, yes?

No, it's the closest node as determined by snitch.sortByProximity.

any given node X will never know whether another node Y has a row
cached or not.  the overhead for communicating that level of detail
would be totally prohibitive.

all caching does is speed the read, once a request is received for
data local to a given node.  no more, no less.

Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support

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