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From Kanak Biscuitwala <kana...@hotmail.com>
Subject RE: Restarting a participant with same configuration
Date Wed, 02 Oct 2013 16:32:38 GMT
One current way to check for non-existence (other than catching HelixException on HelixAdmin#getInstanceConfig)
is to check if HelixDataAccessor#getProperty(keyBuilder.instanceConfig(instanceName) returns

As Kishore said, we will support create if not exists, and it won't throw a RuntimeException.


> Date: Wed, 2 Oct 2013 09:06:37 -0700 
> Subject: Re: Restarting a participant with same configuration 
> From: g.kishore@gmail.com 
> To: user@helix.incubator.apache.org 
> Hi Matthieu, 
> Looks like you setting up the configuration and adding the instance to 
> Helix when the node starts?. Any reason why instances cannot be added 
> to cluster upfront using Helix cli. This way the only thing needed by 
> participant while connecting is instance id. 
> If your application does not allow that, then you should able to check 
> for existing instance before creating new one. 
> We are adding new apis to atomically create if not exists cluster, 
> resource and participant. 
> thanks, 
> Kishore G 
> On Wed, Oct 2, 2013 at 1:49 AM, Matthieu Morel 
> <mmorel@apache.org<mailto:mmorel@apache.org>> wrote: 
> Hi, 
> For a participant to register with Helix, we setup a configuration, 
> then add an instance to Helix with "HelixAdmin#addInstance(clusterName, 
> config);" 
> When a given participant fails / stops and is restarted, it will reuse 
> the same Helix configuration that the failed/stopped instance it 
> replaces (it reads the same config file and runs on the same host 
> etc...). However since Helix kept the previous instance and 
> configuration, it will reject this one (throwing a runtime 
> HelixException). 
> One way to overcome this issue is to capture the exception, drop the 
> instance from Helix (HelixAdmin#dropInstance) and add it again. I'm not 
> sure that's a very appropriate solution though, and was wondering 
> whether there was a better way? 
> Thanks! 
> Matthieu 
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