Comet VS Ajax polling

Question

I need to create a chat like facebook chat.

With Comet I need more memory to keep the connection.

With Ajax polling there is a latency problem if I send request every 3-4 seconds.

So... If the latency ( 3-4 seconds ) doesn't matter, Is Ajax Polling better for my case ?

I think you just answered your own question there :) – Geoff Adams Jun 04 '10 at 15:02 — Geoff Adams, Jun 04 '10 at 15:02

score 6 · Answer 1 · answered Jun 07 '10 at 12:29

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Latency is not the only problem. COMET (long-polling) "saves" your traffic - when you use polling, you cannot know, if there were changes on the server, so some of the calls may be just a waste of traffic and resources (e.g., even if no one's chatting, you're making calls every 3-4 seconds). In case of COMET, you generally need one just call to get an update from the server (with 100% hit rate).

answered Jun 07 '10 at 12:29

Vasil Remeniuk

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but with Comet, I need more memory to keep open the connections... no ? – xRobot Jun 07 '10 at 16:06
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Keeping a connection itself is not so harmful. Memory consumption more depends on what server-side IO API you will chosee - blocking or non-blocking. If you choose the blocking API, you will have a thread per connection -> memory problems with 3-4k open connections. If you choose non-blocking API (almost every application server has NIO capabilities), you can keep millions of opened connection. – Vasil Remeniuk Jun 07 '10 at 16:46
with comet you do not need *much* more memory if you are doing non blocking io – Kaan Yy Sep 24 '13 at 13:47

score 2 · Answer 2 · edited May 23 '17 at 12:08

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@Vasil: "you can keep millions of opened connection"

Take a look to this problem

And regarding the false superiority of NIO over IO.

The iobound article just shows IO outperforms NIO and yes IO goes out of memory before NIO (by the way, the author has not tried to reduce the stack memory with a lower value).

edited May 23 '17 at 12:08

Community

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answered Jan 17 '11 at 14:52

jmarranz

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score 1 · Answer 3 · answered Jun 04 '10 at 15:06

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If latency isn't an issue then AJAX is probably better. Comet can encounter problems maintaining multiple connections between the same client/server pair if you're not very, very careful. (Ref)

answered Jun 04 '10 at 15:06

Quotidian

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Comet VS Ajax polling

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