Push data to page without checking periodically for it?

Question

Is there any way you can push data to a page rather than checking for it periodically?

Obviously you can check for it periodically with ajax, but is there any way you can force the page to reload when a php script is executed?

Theoretically you can improve an ajax request's speed by having a table just for when the ajax function is supposed to execute (update a value in the table when the ajax function should retrieve new data from the database) but this still requires a sizable amount of memory and a mysql connection as well as still some waiting time while the query executes even when there isn't an update/you don't want to execute the ajax function that retrieves database data.

Is there any way to either make this even more efficient than querying a database and checking the table that stores the 'if updated' data OR tell the ajax function to execute from another page?

I guess node.js or HTML5 webSocket could be a viable solution as well?

Or you could store 'if updated' data in a text file? Any suggestions are welcome.

Answer 1

You're basically talking about notifying the client (i.e. browser) of server-side events. It really comes down to two things:

1. What web server are you using? (are you limited to a particular language?)
2. What browsers do you need to support?

Your best option is using WebSockets to do the job, anything beyond using web-sockets is a hack. Still, many "hacks" work just fine, I suggest you try Comet or AJAX long-polling.

There's a project called Atmosphere (and many more) that provide you with a solution suited towards the web server you are using and then will automatically pick the best option depending on the user's browser.

If you aren't limited by browsers and can pick your web stack then I suggest using SocketIO + nodejs. It's just my preference right now, WebSockets is still in it's infancy and things are going to get interesting once it starts to develop more. Sometimes my entire application isn't suited for nodejs, so I'll just offload the data operation to it alone.

Good luck.

Answer 2

Another possibility, if you can store the data in a simple format in a file, you update a file with the data and use the web server to check its timestamp.

Then the browser can poll, making HEAD requests, which will check the update times on the file to see if it needs an updated copy.

This avoids making a DB call for anything that doesn't change the data, but at the expense of keeping file system copies of important resources. It might be a good trade-off, though, if you can do this for active data, and roll them off after some time. You will need to ensure that you manage to change this on any call that updates the data.

It shares the synchronization risks of any systems with multiple copies of the same data, but it might be worth investigating if the enhanced responsiveness is worth the risks.

Answer 3

There was once a technology called "server push" that kept a Web server process sitting there waiting for more output from your script and forwarding it on to the client when it appeared. This was the hot new technology of 1995 and, while you can probably still do it, nobody does because it's a freakishly terrible idea.

So yeah, you can, but when you get there you'll most likely wish you hadn't.