Handout for CSEP 552 lecture 4
Dan Ports <drkp@cs.washington.edu>
Based on notes from MIT course 6.824


        --- Paxos Proposer ---
      	
     1	proposer(v):
     2    while not decided:
     2	    choose n, unique and higher than any n seen so far
     3	    send propose(n) to all servers including self
     4	    if propose_ok(n, na, va) from majority:
     5	      v' = va with highest na; choose own v otherwise   
     6	      send accept(n, v') to all
     7	      if accept_ok(n) from majority:
     8	        send decided(v') to all
      	
        
        --- Paxos Acceptor ---

     9	acceptor state on each node (persistent):
    10	 np     --- highest propose seen
    11	 na, va --- highest accept seen
      	
    12	acceptor's propose(n) handler:
    13	 if n > np
    14	   np = n                        // promise not to accept any
                                         // lower-numbered proposal
    15	   reply propose_ok(n, na, va)
    16   else
    17     reply propose_reject
      	
      	
    18	acceptor's accept(n, v) handler:
    19	 if n >= np
    20	   np = n                       // promise not to accept any
                                        // lower-numbered proposal
                                        
    21	   na = n                       // and make sure that any 
    22	   va = v                       // higher-numbered proposal
                                        // finds out about the value
                                        // we accepted
    23	   reply accept_ok(n)
    24   else
    25     reply accept_reject