The random retry delay for redis session cache was calculated as
rand(100000, 500000) giving an effective retry delay of 100 seconds
to 500 seconds. That's off by a factor of a thousand! Using Redis as a
session cache and when the connection hangs, you can get random
"cannot obtain session lock" errors because it's waiting up to
500 seconds (or about 8.33 minutes) for a Redis connection.
This sets the delay to the originally intended 100ms to 500ms.
(see MDL-59866).
Signed-off-by: Daniel Ziegenberg <daniel@ziegenberg.at>
In 39770792ca read-only sessions were allowed.
In the redis case, as called from the mobile application,
this can lead to returning 'false' for session rather than ''.
There is an edge case whereby redis will fail
to accept connections on the first try but
retrying the connection seems to make it work
Included in this commit:
* Retry functionality in the session init
The redis session handler doesn't use the sessiontimeout config setting
to determine session lifetime.
It has a lock expiry, which is set to 7200 (or a config setting) that is
used to determine how long a lock is held onto, but that should be
distinct from the session timeout.
It is now possible to set up Redis as a session handler for Moodle.
Ensure that the phpredis extension is enabled and working on your sever.
Please place the following lines in config.php
$CFG->session_handler_class = '\core\session\redis';
$CFG->session_redis_save_path = 'tcp://127.0.0.1';
To determine if it has been set correctly, navigate to
$CFG->wwwroot/admin/phpinfo.php and find following the strings in the
session block,
session.save_handler = redis
session.save_path = tcp://127.0.0.1
