I have a application consisting of HTML (AngularJS) client and PHP backend. All communication between client and server is done using XMLHTTPRequests (of course except of loading first HTML file and static resources - JS/CSS...). Server exposes some API endpoints and client makes request to these URL. Once server receives request, it checks $_SESSION to check if user is logged in.
My question is, is it possible that reading (not writing to) from $_SESSION upon almost each request could cause major hangs in responses? For instance, the application works for several requests and then random request is sent and response is received after minutes (15 is record so far). It also seems that the request is processed that late (according to dummy error_log test), so the slowdown is not caused by operations in PHP my code.
Maybe it is a stupid question, but I've already doubled apache's ServerLimit (1000) but no luck. I also have another PHP application on this server which works fine, the only difference I could think of is the working application is barely checking $_SESSION in combination of XMLHTTPRequests.
PHP version: 5.3.3