(php, ajax) How should a server notice something for client?

Question

There are interactive sites (for example this :)) which can notice events without refreshing anything. For example, when I get an answer, a red circle will appear up there. I understand that it can be done with sending ajax requests, say one about every 5 second - but it then would kill servers. Then how should a server send to clients that something changed?

possible duplicate of [AJAX Polling Frequency - To long poll or not to long poll?](http://stackoverflow.com/questions/3842063/ajax-polling-frequency-to-long-poll-or-not-to-long-poll) — JJJ, Jun 01 '12 at 07:41

score 2 · Answer 1 · answered Jun 01 '12 at 07:40

Solutions like socket.io implement different ways to keep the client connected, including:

HTML5 Websockets (New, pretty good, but not supported by older browsers)
Flash plugin (Requires flash plugin, no mobile support)
Long polling (Killer for traditional webservices)

score 1 · Answer 2 · answered Jun 01 '12 at 07:39

1

You can open an XHR that stays alive until the server has a state change to send the response.

This is known as long polling.

answered Jun 01 '12 at 07:39

alex

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but this is still a lot of requesting isnt it? – John Smith Jun 01 '12 at 10:17
I mean, this is still a continuous sending/receiving, overloading the server – John Smith Jun 01 '12 at 10:19

(php, ajax) How should a server notice something for client?

2 Answers2