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What is the best way to program an immediate reaction to an update to data in a database? The simplest method I could think of offhand is a thread that checks the database for a particular change to some data and continually waits to check it again for some predefined length of time. This solution seems to be wasteful and suboptimal to me, so I was wondering if there is a better way. I figure there must be some way, after all, a web application like gmail seems to be able to update my inbox almost immediately after a new email was sent to me. Surely my client isn't continually checking for updates all the time. I think the way they do this is with AJAX, but how AJAX can behave like a remote function call I don't know. I'd be curious to know how gmail does this, but what I'd most like to know is how to do this in the general case with a database. Edit: Please note I want to immediately react to the update in the client code, not in the database itself, so as far as I know triggers can't do this. Basically I want the USER to get a notification or have his screen updated once the change in the database has been made.

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