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Re: Instance ID wrong?
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Re: Instance ID wrong?


  • Subject: Re: Instance ID wrong?
  • From: Anjo Krank <email@hidden>
  • Date: Tue, 2 Dec 2008 13:54:10 +0100

Am 02.12.2008 um 12:09 schrieb Patrick Middleton:

I too have encountered the problem where a stateful request is redirected to a different instance because the requested instance did not respond, and I would strongly welcome an HTTP header or headers being added to indicate to instance the instances which have already not responded to this request.

First of all, as this is a real deployment error, it should be monitor- able somewhere. Probably at the WOAdaptorInfo page or a log file.


Also, I'd have guessed that the only reason an app doesn't respond is that has maxed out the thread pool or sth? When IS it marked dead? By the Adaptor or wotaskd?

That this happens at our sites may also be a network issue that I'm not aware of.

The requested instance (or instances) usually doesn't respond because it's doing a very big database fetch; enabling concurrent request handling usually won't help much as other sessions will likely block waiting for access to the database. lifeabeat interaction with wotaskd should continue unimpeded.

When is the lifebeat sent? I thought it was sent regardless of app state?


How would an instance receiving a stateful request whose URL indicates it should be sent to a different instance make use of some X-WOInstanceDidNotRespond header then? How would the instance know whether the other instance(s) are busy but not dysfunctional, have hung, or have crashed?

This would be the next step. Maybe it could simply redirect the request with some counter attached. Only if it reaches a max, the request is indeed handled by the other instance.


If we really wanted to sort this out, we might be looking at persistent session state shared over all instances, so that any instance could respond to any request, whether stateless or stateful. I would not welcome being asked to implement that myself.

Me neither, and I'm not sure this is possible at all - at least if you are using WO like it's supposed to be, meaning component actions and a lot of new ECs. Otherwise, you could simply write a DA app and only use basic types to store in the session. In that case it should be halfway easy to implement, but then why use WO in the first place.


Cheers, Anjo
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  • Follow-Ups:
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      • From: Andrew Lindesay <email@hidden>
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References: 
 >Instance ID wrong? (From: Anjo Krank <email@hidden>)
 >Re: Instance ID wrong? (From: Andrew Lindesay <email@hidden>)
 >Re: Instance ID wrong? (From: Patrick Middleton <email@hidden>)

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