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From A J <>
Subject R and N
Date Fri, 18 Feb 2011 15:23:21 GMT
Questions about R and N (and W):
1. If I set R to Quorum and cassandra identifies a need for read
repair before returning, would the read repair happen on R nodes (I
mean subset of R that needs repair) or N nodes before the data is
delivered to the client ?
2. Also does the repair happen at level of row (key) or at level of column ?

3. During write, if W is met but N-W is not met for some reason; would
cassandra try to repair N-W nodes in the background as and when it
can. Or the N-W are only repaired when a read is issued ?

4. What is the significance of the 'primary' replica for writes from
usage point ? Writes to primary and non-primary replicas all happen
simultaneously. Ensuring W is decided irrespective of it being primary
or not. Ensuring R is decided by any of the R nodes out of N.
I know the tokens are divided per the primary replica. But other than
that, for read and write operations, do the primary replica play any
special role ?


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