In my migration, I created index as follows:
def self.up
add_index :users, :facebook_id
add_index :references, [:referencing_user_id, :created_at]
....
and
In my migration, I created index as follows:
def self.up
add_index :users, :facebook_id
add_index :references, [:referencing_user_id, :created_at]
....
and