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From Jonathan Ellis <>
Subject Re: Question about cassandra (replication)
Date Thu, 25 Jun 2009 15:17:32 GMT
On Thu, Jun 25, 2009 at 10:10 AM, Harold Lim<> wrote:
> Hi,
> Is the replication factor configurable? For example, Can I configure the replication
factor per column-family (e.g., 5 for column-family a and 3 for column-family b).

It is currently only configurable globally.  It may make sense to
configure on a table/namespace basis.  IMO it does not make sense on a
CF basis.

> Also, I am interested about the replication details. Sandeep wrote:
> "When there's a failure and the #of replicas for a given key goes down,
> Cassandra does not aggressively create a new copy for the data. The
> assumption is that the failed node will be replaced soon enough, and work
> can continue with the other 2 replicas."
> When and how does cassandra replicate when the replication count of a particular data
goes below the replication factor? How does it monitor the replication count of a particular

Currently it re-replicates (repairs) lazily.  This is called "read
repair" and we follow essentially the model given in the Dynamo paper.

Non-lazy repair is being worked on at


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