Sessions occasionally lock each other excessively

[stwalkerster]

https://secure.php.net/manual/en/function.session-write-close.php

session data is locked to prevent concurrent writes only one script may operate on a session at any time

You can reduce the time needed [...] by ending the session as soon as all changes to session variables are done.

session_write_close() ends the session and releases the lock. While this won't help with individual page loads, it should help when multiple pages are loaded at once.

Approaches we could take:

• Switch to using the database for all session data with a custom session handler
• Move all unnecessary session writes (think alerts) to the database

[stwalkerster]

Page load started while a different long page load was in progress.

[stwalkerster]

We have quite a few examples of this now from production:

[stwalkerster]

I did some work on this to move sessions to redis, but there were definite concurrency issues at play.