session_start hangs

Question

since a few hours our server hangs every time you do a session_start.

For testing purposes i created a script which looks like this:

Answer 1

Just put session_write_close(); befor Session_start();

as below:

<?php
    session_write_close();
    session_start();
    .....
?>

Answer 2

I had a weird issue with this myself.

I am using CentOS 5.5x64, PHP 5.2.10-1. A clean ANSI file in the root with nothing other than session_start() was hanging. The session was being written to disk and no errors were being thrown. It just hung.

I tried everything suggested by Thariama, and checked PHP compile settings etc.

My Fix:

yum reinstall php;  /etc/init.d/httpd restart

Hope this helps someone.

To everyone complaining about the 30 seconds of downtime being unacceptable, this was an inexplicable issue on a brand new, clean OS install, NOT a running production machine. This solution should NOT be used in a production environment.

Answer 3

I don't know why, but changing this value in /etc/php/7.4/apache2/php.ini worked for me:

;session.save_path = "/var/lib/php/sessions"
session.save_path = "/tmp"

Answer 4

The problem: -

Iv experienced (and fixed) the problem where file based sessions hang the request, and database based sessions get out of sync by storing out of date session data (like storing each session save in the wrong order).

This is caused by any subsequent request that loads a session (simultaneous requests), like ajax, video embed where the video file is delivered via php script, dynamic resource file (like script or css) delivered via php script, etc.

In file based sessions file locking prevents session writing thus causing a deadlock between the simultaneous request threads.

In database based session the last request thread to complete becomes the most recent save, so for example a video delivery script will complete long after the page request and overwrite the since updated session with old session data.

The fix: -

If your ajax or resource delivery script doesnt need to use sessions then easiest to just remove session usage from it.

Otherwise you'd best make yourself a coffee and do the following: -

1. Write or employ a session handler (if not already doing so) as per http://www.php.net//manual/en/class.sessionhandler.php (many other examples available via google search).

2. In your session handler function write() prepend the code ...

       // processes may declare their session as read only ...
       if(!empty($_SESSION['no_session_write'])) {
               unset($_SESSION['no_session_write']);
               return true;
       }
   

3. In your ajax or resource delivery php script add the code (after the session is started) ...

       $_SESSION['no_session_write'] = true;
   

I realise this seems like a lot of stuffing around for what should be a tiny fix, but unfortunately if you need to have simultaneous requests each loading a session then it is required.

NOTE if your ajax or resource delivery script does actually need to write/save data, then you need to do it somewhere other than in the session, like database.

Answer 5

If this helps:

In my scenario, session_start() was hanging at the same time I was using the XDebug debugger within PHPStorm, the IDE, on Windows. I found that there was a clear cause: Whenever I killed the debug session from within PHPStorm, the next time I tried to run a debug session, session_start() would hang.

The solution, if this is your scenario, is to make sure to restart Apache every time you kill an XDebug session within your IDE.