title: xSpanner: how leader sync data to replicas?
body: <p>In <a href="http://research.google.com/archive/spanner.html" rel="nofollow">Spanner: Google’s Globally-Distributed Database</a>, section 2.1, we read:</p>
  
  <blockquote>
    <p>To support replication, each spanserver implements a single Paxos state machine on top of each tablet. (An early Spanner incarnation supported multiple Paxos state machines per tablet, which allowed for more flexible replication configurations. The complexity of that design led us to abandon it.)</p>
    
    <p>The Paxos state machines are used to implement a consistently replicated bag of mappings.</p>
  </blockquote>
  
  <p>Does this single Paxos state machine is similar as "Paxos Made Simple" mentioned Paxos state machine? </p>
  
  <p>I'm curious about once a new leader elected how to learn all the data which is lost. Anyone can describe the detail implementation of Paxos group in Spanner?</p>