The changes are covered by unit tests. Setup Install the PHP Redis extension (replace " X " as your server's PHP version, e.g. 8.0) sudo apt update && sudo apt install -y phpX-redis Restart your web server. Confirm the redis PHP extension is enabled: " php -i | grep redis " - You should see a bunch of lines related to redis. Install redis. e.g. using Docker docker run --name redis -p 6379:6379 -d redis Setup redis as the session handler, e.g. copy the following to your config.php: $CFG ->session_handler_class = '\core\session\redis' ; $CFG ->session_redis_host = '127.0.0.1' ; $CFG ->session_redis_port = 6379; $CFG ->session_redis_acquire_lock_timeout = 2; Install the session breaker plugin to help with testing: git clone https://github.com/catalyst/moodle-tool_sessionbreaker/ admin/tool/sessionbreaker Test Visit this page, which will lock the session for 20 seconds: /admin/tool/sessionbreaker/bad.php?wait=20 In a second tab immediately load this page: /admin/tool/sessionbreaker/good.php Confirm after roughly 2 seconds it throws an exception eg Unable to obtain session lock for sid: pvga0j242m within 0 days 0 hours 0 minutes 2 seconds. It is likely that another page ([pid 1758327] workstation:/admin/tool/sessionbreaker/bad.php?wait=20), possibly in another browser tab, has caused this due to any of the following reasons: it has a long session lock; or the session lock was never released due to an error. You can try to close and re-open your browser or wait until the session lock timeout (0 days 20 hours 0 minutes 0 seconds) has passed. If this error persists, please notify the server administrator.