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From Ben Hall <...@zynga.com>
Subject Re: An interesting problem removing a key
Date Fri, 02 Sep 2011 16:22:54 GMT
Yeah - I guess to explain a little more... we have a very large number of clients out in the
wild that in essence going to each pool of clients would be a huge hassle and pain.  So -
yes we could update our client and provide a watcher switch but it would be very cumbersome
to get to and update each of the clients.  We could also change the ZK structure - but again
we would have to change all of the clients in the wild - a step we are trying to avoid. 

In short we were looking for just a quick workaround or hack from the server ensemble perspective
even though it may not be a supported or recommended function - this would be just a one time
thing for us.


On Sep 2, 2011, at 12:22 AM, Ted Dunning wrote:

> I would recommend not spending a whole lot of time figuring out how to make
> Zookeeper lie to the clients.  It is hard enough to make distributed
> software that tells the truth.
> Why don't you just make the ZK structure match what you are trying to do?
> For instance, have a znode containing the key and a separate znode that is
> just for watching.  Then the server has the option of updating both znodes
> or just the key depending on what behavior you want to get.
> This is simple and straightforward and makes it very clear what you mean to
> do.  Why hack the server for such a thing?
> On Fri, Sep 2, 2011 at 1:37 AM, Mahadev Konar <mahadev@hortonworks.com>wrote:
>> Ben,
>> I dont think I fully understand the use case. Is it possible that you
>> can register a different callback for that key?
>> Something like:
>> zk.exists(String path, Watcher watcher)
>> where you can register a different watcher for this path?
>> Would this work?
>> mahadev
>> On Thu, Sep 1, 2011 at 5:58 PM, Ben Hall <ben@zynga.com> wrote:
>>> Hi,
>>> We have an interesting problem use case that we wanted to ping the group
>> about.
>>> We have a Key on all of our Ensemble servers.  All of our clients are
>> also subscribed to this key.  We want to remove the key from the ensemble
>> servers without this action getting propagated down to the clients.  Or if
>> it does get propagated down - at a minimum we do not want to watch callback
>> function to be called.
>>> Is there a way to in essence sever the watches from the server
>> perspective without the client knowing?
>>> We are investing looking into the hidden keys on the zookeeper servers
>> that hold the list of watches and possibly editing that key.  has anyone
>> done that before?  Do we know what happens when that key is edited manually?
>>> Any other suggestions or possibilities available to us?
>>> Thanks
>>> Ben

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