Whenever I send more than 1 paralel ajax request at a time to my backend, some respond within a reasonable timeframe (<100ms), however some of the requests hang for approximately 1s before returning a response, regardless of which order they are executed in.
I have decided to test this out by creating a very simple HTML+jQuery/PHP (frontend+backend) script which creates 6 paralel ajax requests and running it both on my local server, as well as Digitalocean’s server using the same setup (Debian 10 Apache + PHP 7.4).
The results on local server:
The results on Digitalocean server:
The javascript:
function ajaxAtOnce() {
$.get("ajax1.php", function (data) {
console.log(data);
});
$.get("ajax2.php", function (data) {
console.log(data);
});
$.get("ajax3.php", function (data) {
console.log(data);
});
$.get("ajax4.php", function (data) {
console.log(data);
});
$.get("ajax5.php", function (data) {
console.log(data);
});
$.get("ajax6.php", function (data) {
console.log(data);
});
}
PHP endpoints (all equal):
<?php
// return 100 randomly ordered numbers
$array = range(1,100);
shuffle($array);
echo json_encode($array);
Important notes
- If I hardcode a large enough “timeout” inbetween ajax requests, I get a response within expected timeframe:
function ajaxWithTimeout() {
setTimeout(function() {
$.get("ajax1.php", function (data) {
console.log(data);
});
}, 1000);
setTimeout(function() {
$.get("ajax2.php", function (data) {
console.log(data);
});
}, 2200);
setTimeout(function() {
$.get("ajax3.php", function (data) {
console.log(data);
});
}, 3500);
setTimeout(function() {
$.get("ajax4.php", function (data) {
console.log(data);
});
}, 4700);
setTimeout(function() {
$.get("ajax5.php", function (data) {
console.log(data);
});
}, 5900);
setTimeout(function() {
$.get("ajax6.php", function (data) {
console.log(data);
});
}, 7100);
}
-
If I send all the requests to the same endpoint (ajax1.php for example), there is no problem
-
After some research I found 2 server parameters that seem to be mentioned with regards to this issue, but they are set to their default values, and removing the limit does not have an effect:
RateLimitInterval=30s, RateLimitBurst=1000
As you can imagine, this issue can be very frustrating, especially when developing a SPA in a JS framework like React, which is where I first noticed the issue.
