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From Flavio Junqueira <...@yahoo-inc.com>
Subject Re: Zookeeper WAN Configuration
Date Fri, 24 Jul 2009 23:50:18 GMT
Just a few quick observations:

On Jul 24, 2009, at 4:40 PM, Ted Dunning wrote:

> On Fri, Jul 24, 2009 at 4:23 PM, Todd Greenwood
> <toddg@audiencescience.com>wrote:
>
>> Could you explain the idea behind the Observers feature, what this
>> concept is supposed to address, and how it applies to the WAN
>> configuration problem in particular?
>>
>
> Not really.  I am just echoing comments on observers from them that  
> know.
>

Without observers, increasing the number of servers in an ensemble  
enables higher read throughput, but causes write throughput to drop  
because the number of votes to order each write operation increases.  
Essentially, observers are zookeeper servers that don't vote when  
ordering updates to the zookeeper state. Adding observers enables  
higher read throughput affecting minimally write throughput (leader  
still has to send commits to everyone, at least in the version we have  
been working on).

>
>> """
>> The ideas for federating ZK or allowing observers would likely do  
>> what
>> you
>> want.  I can imagine that an observer would only care that it can see
>> it's
>> local peers and one of the observers would be elected to get updates
>> (and
>> thus would care about the central service).
>> """
>> This certainly sounds like exactly what I want...Was this  
>> introduced in
>> 3.2 in full, or only partially?
>>
>
> I don't think it is even in trunk yet.  Look on Jira or at the  
> recent logs
> of this mailing list.

It is not on trunk yet.

-Flavio


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