Comment 4 for bug 1882205

Reviewed: https://review.opendev.org/742664
Committed: https://git.openstack.org/cgit/openstack/charm-mysql-innodb-cluster/commit/?id=5eb43790d4d33671edd8613558043150a84f3135
Submitter: Zuul
Branch: master

commit 5eb43790d4d33671edd8613558043150a84f3135
Author: Dmitrii Shcherbakov <email address hidden>
Date: Thu Jul 23 16:21:22 2020 +0300

    Set expel timeout to 5 seconds

    Focal has MySQL version 8.0.20-0ubuntu0.20.04.1 which sets
    group_replication_member_expel_timeout to 0 by default [0]. As a result,
    cluster members are expelled from the cluster 5 seconds after the loss
    of connectivity.

    This proves to be too short for our CI and some other environments in
    the wild.

    MySQL documentation for this option suggests that 5 or even 10 seconds
    may be too low for congested or overcommitted environments which happens
    to be the case. As of MySQL 8.0.21 the default for
    group_replication_member_expel_timeout is set to 5 seconds.

    [0] https://dev.mysql.com/doc/refman/8.0/en/group-replication-options.html#sysvar_group_replication_member_expel_timeout
    [1] https://dev.mysql.com/doc/refman/8.0/en/group-replication-responses-failure-expel.html

    Change-Id: Ia33c6263e616657d21b41fcf1a8abfb34e6cb58d
    Partial-Bug: #1882205