Detecting and pushing a stream of events to a web browser (HTML5, PHP, PostgreSQL)?

My currently in-development website is written in PHP. As users are using the site, they'll be performing actions and I'd like to be able to push notifications of these actions to other users that they're connected to.

Now while I'm sure that using EventSource and a PHP document to server up the appropriate data: lines would work, I've got absolutely no idea how I should notify that PHP document when a new message actually needs to be sent.

What I essentially mean is that when an action takes place, there will be an entry into the PostgreSQL database with the message information (such as the action that was taken). However, it's not efficient to have each instance of the "messaging" PHP document (the one that EventSource is connected to) to continuously poll PostgreSQL for new messages. With 50 users active at once, that would be 50 instances polling PostgreSQL, and as you can probably see, not a very efficient use of resources.

So I'm wondering whether anyone has any suggestions as to software that might assist with this problem. Ideally I'd like to be 开发者_如何学JAVAable to call a function that indicates an action has been undertaken, which is then sent all the other instances of "messaging" PHP document so that they can interpret the message and see whether it's relevant and push it back to the client.

Essentially I need a way to notify running PHP instances (that were started via Apache) of a new message being created, by calling a function in another PHP instance with the message information. I don't need assistance with getting the messages to the client; I can do that with EventSource.

Does anyone have any suggestions as to how this task could be undertaken?

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Conventional ways of solving the problem are using a java applet (which can open a socket back to the originating server) or using long polling (e.g. comet).

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I've succeeded in doing this by using memcache with a messages-count key-value and a message-$i key-value where $i is an incrementing number. A PHP document is connected to via long polling and it continuously checks to see whether message-$(messages-count) exists, in which case it returns it.

There's a bit more to this since it will return multiple messages if they're created at once and also can load the initial checking number ($i) as a $_GET parameter, but this is essentially how it works. It's near instant and new messages can easily be added to memcache via PHP (each time you create a new message, you increment messages-count).

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Take a look at php mem sharing