Hi Flavio,

Thank you for the information. 

So how do you handle than the following scenario?
You have 5 servers and temporary network segmentation, where server 1 and 2 
cannot talk to 3,4 and 5. Will server 1 and 2 do a new leader election for 
their partition, as well server 3,4 and 5 for their partition? If yes, how do 
they synchronize if they can reach each other again?  

Mit freundlichen Grüßen / With best regards 
Thomas Kießlich 

Siemens Enterprise Communications GmbH & Co. KG 
HiPath Applications 

Schertlinstr. 8
81379 Munich, Germany 

-----Ursprüngliche Nachricht-----
Von: Flavio Junqueira [mailto:[EMAIL PROTECTED] 
Gesendet: Montag, 17. November 2008 13:49
An: zookeeper-user@hadoop.apache.org
Betreff: RE: Dynamic server management?

Hi Thomas, We currently don't have such a feature of adding and removing
servers dynamically, although we would like to, so we'll have it eventually.

Without a dynamic mechanism for adding and removing servers, your example is
problematic. Suppose that you configure your ensemble to have 3 servers, and
then you start only one. Your single server would say: "Hey, I'm alone so I
should make progress independently". This is reasonable, right? Well, not
really, because you can have the following alternative execution. You start
your three servers, but there is a temporary network partition and server 1
cannot talk to servers 2 and 3. Consequently, server 1 will make progress
independently of 2 and 3, and their state will diverge.

Hope it helps.


> -----Original Message-----
> From: Kiesslich, Thomas [mailto:[EMAIL PROTECTED]
> Sent: Monday, November 17, 2008 11:46 AM
> To: zookeeper-user@hadoop.apache.org
> Subject: Dynamic server management?
> Hi all,
> I am evaluating ZooKeeper as a discovery protocol. I want to change the
> number of servers that build up  ensemble during runtime of an existing
> number servers. Is that possible or do I have to change the configuration
> and restart all servers? I found that if you have 3 servers configured and
> startup the first it is continously looking for the at least one other
> server. Is it really necessary to do that? If the first server does not
> find anyone else, it could elect itself as the leader. If the next server
> starts up the can redo the election I guess.
> Could you please help me with these questions? Thank you.
> Mit freundlichen Grüßen / With best regards
> Thomas Kießlich
> Siemens Enterprise Communications GmbH & Co. KG
> HiPath Applications
> Schertlinstr. 8
> 81379 Munich, Germany
> Phone: +49 (89) 722-32483
> Fax: +49 (89) 722-40560
> Communication for the open minded
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