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From Henry Robinson <he...@cloudera.com>
Subject Re: Dynamic servers addition and persistent storage.
Date Wed, 01 Jul 2009 14:46:32 GMT
Hi Maxime -

When a quorum of ZooKeeper servers have failed, the service stops being
available - you cannot write or read to any item. Once a quorum returns to
operation, the ensemble recovers automatically and continues where it left
off. There is the same requirement that a quorum of servers must see every
write.

We (and myself in particular) are working on dynamic cluster membership, see
https://issues.apache.org/jira/browse/ZOOKEEPER-107 and the related
https://issues.apache.org/jira/browse/ZOOKEEPER-368.

Henry

On Wed, Jul 1, 2009 at 3:07 PM, Maxime Caron <maxime.caron@gmail.com> wrote:

> I was investigating scalaris (http://code.google.com/p/scalaris/) but
> found
> it does not support a persistent storage.
> In their faq they say it cant be done because they assume that a majority
> of
> the replicas of an item is always available.
> If this precondition is violated, a majority of the nodes with replicas of
> an item x is not available, the item cannot be changed. It is lost.
> Persistent storage cannot help directly.
> So i would like to understand if zookeeper work the same way or their is a
> recovery model for  when the majority of the goes down and then back up.
>
>
> Unlike zookeeper with scalaris servers can be added or removed on the fly
> without any service downtime.
> From what i can understand in zookeeper you need to have a fixed server
> list
> that every body share.
> Would it be possible to add on the fly server addition and removal to
> zookeeper?
>

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