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

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
want.  I can imagine that an observer would only care that it can see
local peers and one of the observers would be elected to get updates
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.


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