Server->Client communication with php/mysql/jquery

Here is what I am trying to make happen:

Anytime there is an update to a certain variable in my database, I would like that new variable to be sent to any client logged into my site and automatically update asynchronously on their page.  Is there a way to asynchronously have the client's browser be constantly checking that variable/variables in the database to see if they have changed with PHP/JQuery?  What is the best way to handle something like this?
ncotherman2Asked:
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ramelongConnect With a Mentor Commented:
Well, depends on the delay between readings... and the amount of logged users.

If these variables aren't required until the reload, the best you can do is read them at the begining of the PHP program. In any other case, you need a timer triggered reader...

In order to update javascript variables, needed to modify vehaviours on the client, a practical way is to linking the reading action to a button action, for instance, you may read the variables  (with AJAX) every time the user clicks on the icons or buttons (for this you may use the onClick event in those elements).

Remember that PHP variables are used at server side, and javascript variables are used at client side.
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ramelongCommented:
To develop a, efficient method, firstly there some things to know:
- How these variables are updated?
- How you currently know who is logged and who don't?
- These variables to e updated at client side: in which language are working? In javascript?

But on the other hand you may check these variables in several ways:
- Every time the page is loaded (or reloaded).
- With a timer in javascript (unrecomended on IE because of the "tick" sound).
- With a timer in javascript that check a php program into a layer. This program must have to update the variables.
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ncotherman2Author Commented:
The database variables are updated by other users on the site.

Yes I currently know who is logged on.

Right now I am retrieving the variables with php.


So in order to be constantly checking these variables I would need to have a constantly running Javascript loop?  Wouldn't that significantly affect performance?
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ramelongCommented:
Good luck with your project!
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