When a backup (or restore) is in progress and the user
has another tab open that is taking time to generate and
holding the session lock, a condition arises where
multiple ajax calls are "queued" because the long page
is holding the session lock. When this lock is released,
the queued ajax requests complete. However, as the ajax
requests also lock this can block other requests until they
complete. This patch decreases the frequency of ajax calls
and stops them from holding the session lock.
This patch adds asynchronous backup and restore functionality
to Moodle. This is an optional feature and is not enabled by
default. It can be enabled by site administrators.
Asynchronous backup and restores are actioned by the Moodle
adhoc task API. The progress of backup and restores is
displayedin the Moodle UI. Users can also be sent a message
when a backup or restore operation completes via the
Moodle messaging API.
