A few times a day, when our website is busy, we have more than 1000 requests per second on our database.
During these busy times, when a user clicks on an element and makes an AJAX call and then clicks another element and makes another AJAX call, the second call will wait for the response of the first call.
How can I have this AJAX calls run simultaneously? Is this time space between two calls because of the server being busy? If yes, how can we handle simultaneous AJAX calls?
I had similar problem as you do in the past. Then it was open session on server side. Even if ajax call was async, then it have to wait for server because of lock on session file.
Try to close session write when you do not write anything and then, check you ajax again. Here you have reference to proper method: session_write_close