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To facilitate state in web apps, PHP provides a session handling mechanism.
Read more about PHP session handling at https://www.php.net/manual/en/book.session.php
That means if there are three ajax requests to the server, request two and three will be blocked waiting on the request in front of them.
To get it running all we need to do is update two lines in the php.ini file to instruct PHP to use Redis and where to find the Redis server. I will not cover how to set up a Redis server in this article.