My site checks the database for overdue reminders by making an AJAX request every 5 seconds. I've been told this is not ideal because of too many AJAX calls, one person said it's almost like DDOSing your own site if there are many people on with several tabs open etc.
The alternatives are using websockets or ajax-long-pulling. I can't use websockets because my shared hosting doesn't have that capability. Ajax-long-pulling is not ideal because of limited connections.
So a workaround I thought of would be to have a file on the server which simply stores a token. The browser reads this file via a hidden i-frame every 5 seconds, and if something relevant changes in the database the token is changed and this signals the browser to send an AJAX request to get the new reminders.
Would that be a feasible workaround to significantly reduce the load on the server since it's not making so many AJAX calls every 5 seconds since it's just reading the file instead?
"one person said it's almost like ..." - was that person the system administrator of the host where your site runs?
"because my shared hosting doesn't have that capability" - if writing lots of code is cheaper than switching web providers then you really need to look at your at the way you manage your hosting.
"Ajax-long-pulling is not ideal because of limited connections" - and you think the same problem would not apply to websockets?
You seem to be trying to fix a problem you don't know exists. And you don't seem to be in a position to evaluate whether any changes you make will have the desired effect.
After discounting comet and websockets, your only option for reducing the impact on the server is to reduce the frequency of polling. But your next step should be to get establish a capability to assess what impact the facility currently has on the server and how that changes if you change the behaviour. This can be rather tricky on a shared host - at best you're going to see a lot of noise generated by other tenants, but if you really were consuming a lot of resources, I'm quite confident that a competent hosting provider would be alerting you to this.