Unable to obtain session lock

"Unable to obtain session lock"

Moodle makes use of PHP sessions to track authenticated user sessions. These sessions are locked by each request to avoid data loss across processes serving requests. Unfortunately, by default Moodle holds this session lock for the duration of a request, compounding the problem by using the session as a cache storage backend, preventing other requests from being processed.

In the meantime stuck sessions can be worked around by removing the MoodleSession cookie as follows.

Chrome

1. Hit F12 to open DevTools.
2. Click Application across the top bar.
3. Expand Cookies in the sidebar.
4. Right-click the domain for the affected platform and click Clear.

Firefox

1. Hit F12 to open developer tools.
2. Click Storage across the top bar.
3. Expand Cookies in the top bar.
4. Right-click the domain for the affected platform and click Delete All.