[nanomsg] Re: Where "Channel ID" are managed in the code ?
- From: Martin Sustrik <sustrik@xxxxxxxxxx>
- To: nanomsg@xxxxxxxxxxxxx
- Date: Tue, 14 Jan 2014 21:24:17 +0100
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Hi Laurent,
> 1. Add new socket option, say NN_REQ_SCHEDULER, with possible
> values of NN_REQ_ROUND_ROBIN (current implementation, the default)
> and NN_REQ_STICKY. The latter, when applied to a REQ socket would
> cause requests from the same client to be sent, if possible, to the
> same worker. If the old worker is not available, the message will
> be sent to a different worker.
>> In my use case, if the message is sent to a different worker, it
>> will fail as it is stateful. So the best way here is to drop the
>> message IMO. I think NN_REQ_STICKY is useful only for statefull
>> messaging. And in statefull processing, reassigning one peer to
>> another fails anyway, or you have to add some management to
>> reinitialize the exchange from the beginning. It is useless
>> complexity. It is not only performance optimisation to use cache
>> data as most as possible. Here, I have no mean to recover from
>> the new worker. But probably there is the need for two different
>> behaviours of NN_REQ_STICKY. I will do it with a simple drop.
The behaviour that I have described is actually used in some
large-scale applications. The request is routed to a worker which
accesses the shared data using some kind of distributed DB/filesystem
(think of GFS). The filesystem either has the data cached locally or
has to load them from a different node. By assigning requests from the
same client to the same worker you are maximising the chance of the
former and thus improving the efficiency of the system.
In your use case, I would suggest that the worker that doesn't have
the data just returns a reply saying "no data" at the application
level. There's no much point of handling the check on nanomsg level IMO.
Martin
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