session_create_id() fails when an active session exists

[ellotheth]

PHP 7.4.15
Memcached 3.1.5
libmemcached 1.0.18
Test script and config details: https://gemma.wonderproxy.com/session.php

I'm using Memcached to back my login sessions (session.save_handler=memcached). I don't have session locking enabled (memcached.sess_locking=Off). session_create_id() works when there is no active session, and fails with a warning when there is an active session:

Warning:  session_create_id(): Failed to create new ID

If I swap to session.save_handler=files, session_create_id() works as expected in both cases. Session operations outside of session_create_id() work as expected (it's currently powering logins with no warnings or other errors).

I'm not sure if the problem is on my side or the Memcached side, so any insight would be much appreciated. If you need more information, let me know.

[heldchen]

experiencing the same on 8.0 - were you able to work around this?

[ellotheth]

were you able to work around this?

Nope. In our case there's a "graceful" fallback, so I set up our log monitors to ignore this warning. 🤷‍♀️

[heldchen]

oh well. thanks! my workaround is to keep using redis as the session storage, which works fine with session_create_id() for already active sessions.