Comments in line:

On 8/5/09 12:10 PM, "Todd Greenwood" <> wrote:

> Flavio/Patrick/Mahadev -
> Thanks for your support to date. As I understand it, the sticky points
> w/ respect to WAN deployments are:
> 1. Leader Election:
> Leader elections in the WAN config (pod zk server weight = 0) is a bit
> troublesome (ZOOKEEPER-498)
Yes, until ZOOKEEPER-498 is fixed, you wont be able to use it with groups
and zero weight.

> 2. Network Connectivity Required:
> ZooKeeper clients cannot read/write to ZK Servers if the Server does not
> have network connectivity to the quorum. In short, there is a hard
> requirement to have network connectivity in order for the clients to
> access the shared memory graph in ZK.

> Alternative
> -----------
> I have seen some discussion about in the past re: multi-ensemble
> solutions. Essentially, put one ensemble in each physical location
> (POD), and another in your DC, and have a fairly simple process
> coordinate synchronizing the various ensembles. If the POD writes can be
> confined to a sub-tree in the master graph, then this should be fairly
> simple. I'm imagining the following:
> DC (master) graph:
> /root/pods/1/data/item1
> /root/pods/1/data/item2
> /root/pods/1/data/item3
> /root/pods/2
> /root/pods/3
> ...etc
> /root/shared/allpods/readonly/data/item1
> /root/shared/allpods/readonly/data/item2
> ...etc
> This has the advantage of minimizing cross pod traffic, which could be a
> real perf killer in an WAN. It also provides transacted writes in the
> PODs, even in the disconnected state. Clearly, another portion of the
> business logic has to reconcile the DC (master) graph such that each of
> the pods data items are processed, etc.
> Does anyone have any experience with this (pitfalls, suggestions, etc.?)
As far as I understand is that you mean that have a master Cluster with
other in a different data center syncing with the master (just a subtree)?
Is that correct? 

If yes, this is what one of our users in Yahoo! Search do. They have a
master cluster and a smaller cluster in a different datacenter and a brdige
that copies data from the master cluster (only a subtree) to the smaller one
and keeps them in syncs.

> -Todd

Reply via email to