[Seaside] Comet

Colin Putney cputney at wiresong.ca
Thu Oct 15 18:03:53 UTC 2009

On 15-Oct-09, at 10:50 AM, Robert Sirois wrote:

> Am I correct in my understanding that Comet only works when  
> something changes serverside? Say, one client increments a counter  
> (as per the example), then the server pushes the new value to all  
> connected clients.
> Is there a way that Comet can be set up to push information every so  
> often? This way being independent from any user input.

If you want to do periodic updates, I would recommend having the  
clients poll, rather than using Coment.

Comet is good for the case where you have events occurring at  
unpredictable times and you need to push notification of them out to  
all clients. In this case polling, is inefficient because you're  
either wasting resources by checking for events when there aren't any,  
or introducing latency when there is a new event but you're waiting  
for the next poll. There's a trade-off between efficiency and latency  
- the more frequently you poll the more resources you waste, but the  
less frequently you poll, the more latency you introduce. Comet solves  
this by using fewer HTTP requests, and sending events as they occur.

If I understand your situation correctly, you want to update clients  
on a regular schedule. It's not a counter so much as a clock that's  
being updated. In this case, polling is quite efficient. You know when  
there will be new data, so you just have to schedule the clients to  
poll at those times - high efficiency and low latency.


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