Examples:
class User < ActiveRecord::Base
include MixedGauge::Model
use_cluster :user
def_distkey :email
replicates_with slave: :UserReadonly, backgroud: :UserBackground
end
User.put!(email: '[email protected]', name: 'alice')
alice = User.get('[email protected]')
alice.age = 1
alice.save!
User.all_shards.flat_map {|m| m.where(name: 'alice') }.compact