By default Postgresql first restores the data and then the indexes when dumping and restoring the database.
Restoring index activities_visibility_index took a very long time.
users_ap_id_COALESCE_follower_address_index was later added because having this could speed up the restoration tremendously.
The problem now is that restoration apparently happens in alphabetical order, so this new index wasn't created yet
by the time activities_visibility_index needed it.
There were several work-arounds which included more complex steps during backup/restore.
By renaming this index, it should be restored first and thus activities_visibility_index can make use of it.
This speeds up restoration significantly without requiring more complex or unexpected steps from people.
ilja