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From Benjamin Reed <br...@yahoo-inc.com>
Subject Re: ephemeral node after server bounce
Date Thu, 04 Feb 2010 22:34:49 GMT
i second ted's proposals! thanx ted.

there is one other option. when you create the ZooKeeper object you can 
pass a session id and password. your bounced server can actually 
reattach to the session. (that is why we put that constructor in.) to 
use it you need to save the session id and password to a persistent 
store (a file) when you first attach, and then when you restart read the 
id and password from the file.

ben

Ted Dunning wrote:
> On Thu, Feb 4, 2010 at 2:20 PM, Yonik Seeley <yonik@lucidimagination.com>wrote:
>
>   
>> There's no way to "hand over" responsibility for an ephemeral znode, right?
>>
>>     
>
> Right.
>
>
>   
>> We have solr nodes create ephemeral znodes (name based on host and port).
>> The ephemeral znode takes some time to remove of course, so what
>> happens is that if I bounce a solr server (containing a zk client) the
>> ephemeral node will still exist when the server comes back up.
>>
>>     
>
> This problem comes up with any system that has hysteresis and needs a single
> point of control.
>
>
>   
>> What's the best way to handle this situation?  Delete and re-create?
>>
>>     
> Watch it and re-create when it does disappear?
>   
>
> I think you need to handle the problem of multiple search nodes coming up on
> the same machine, possibly because the old one may have hung up.
>
> So... I would recommend
>
> a) if the ephemeral still exists, wait for a few more seconds to see if it
> disappears (20?)
>
> b) if it goes away, create a new one and continue as normal
>
> c) if it doesn't go away take additional action to determine if service is
> still running (i.e. panic and run in circles).
>   


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