Comment 3 for bug 1968686

This is similar to LP#1968688.
I think this issue is due to the old percona-cluster charm (r279) not compatible with new Juju (2.9.x).
To reproduce,
- deploy juju controller 2.8 and add a new 2.8 model
- deploy percona-cluster r279
- upgrade juju controller and model to 2.9.x
- deploy a new application, e.g. trilio, which has a relation with percona-cluster
- trilio fails to run some hook and ends up with 'shared-db' incomplete message in juju status
So we need to upgrade percona-cluster charm to r302.
Then trilio can finish db relation hook after a while.
If not, remove shared-db relation and add it again.
Again probably not worth updating the old charm to work with new juju.
Just put a note here for others who meet the same issue.