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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Question about node failure...
Date Mon, 29 Mar 2010 17:32:48 GMT
On Mon, Mar 29, 2010 at 12:27 PM, Ned Wolpert <ned.wolpert@imemories.com> wrote:
> Folks-
>
> Can someone point out what happens during a node failure. Here is the
> Specific usecase:
>
>   - Cassandra cluster with 4 nodes, replication factor of 3
>   - One node fails.
>   - At this point, data that existed on the one failed node has copies on 2
> live nodes.
>   - The failed node never comes back
>
> First question: At what point does Cassandra re-migrate that data that only
> exists on 2 nodes to another node to retain the replication factor of 3?

When you tell it to decommission the dead one.

> Second question: Given the above case, if a brand new node is added to the
> cluster, does anything happen to the data that now only exists on 2 nodes?

No, Cassandra doesn't automatically assume that "this node is never
coming back" w/o intervention, by design.  (Temporary failures are
much more common than permanent ones.)

-Jonathan

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