关于paxos的问题

hyx2011

2015/9/15镜像同步13 回复

实在不知道发哪个版，只好发这个版了再刷MIT的6.824，里面在讲paxos得时候，给出的acceptor的伪代码如下： acceptor's prepare(n) handler: if n > np np = n reply prepare_ok(n, na, va) else reply prepare_reject 其中na和va是acceptor记录的最高的n和v。为什么acceptor需要将n和v返回给proposer？感觉proposer不需要这些啊？

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9 条回复

ylewxh机器人#1 · 2015/9/15

bd一个，看paxos好几次了还不明白

shixiaotian机器人#2 · 2015/9/25

不把当前的最大值发给proposer，proposer怎么知道应该发什么才能让acceptor同意呢？

aiquestion机器人#3 · 2015/9/25

Orz。。。有啥相关推荐读物或视频么？【在 shixiaotian 的大作中提到: 】 : 不把当前的最大值发给proposer，proposer怎么知道应该发什么才能让acceptor同意呢？

lizz机器人#4 · 2015/9/25

You can see proposer's handler in 6.824 web proposer(v): while not decided: choose n, unique and higher than any n seen so far send prepare(n) to all servers including self if prepare_ok(n, n_a, v_a) from majority: v' = v_a with highest n_a; choose own v otherwise send accept(n, v') to all if accept_ok(n) from majority: send decided(v') to all ----------------------------------------- so, if acceptor's accpted number > proposer's accepted number, the proposer should update its accepted number and accepted value

hyx2011机器人#5 · 2015/9/25

但是就算不发给proposer，提出最大值的proposer在收到大部分acceptor的prepare_ok之后也会发送accept给acceptor，协议也可以完成。发给proposer会让获得返回值的proposer发送重复的消息给acceptor，这不会浪费网络IO么？【在 shixiaotian 的大作中提到: 】 : 不把当前的最大值发给proposer，proposer怎么知道应该发什么才能让acceptor同意呢？

hyx2011机器人#6 · 2015/9/25

But I don't think proposer need to update its n and v. The accepted number and value seems useless for proposer 【在 lizz 的大作中提到: 】 : You can see proposer's handler in 6.824 web : proposer(v): : while not decided: : ...................

lizz机器人#7 · 2015/9/25

If there is only one proposer, you're right. But, There may be many proposers at the same time, so they must record the accepted value, otherwise these proposer only known the propose has been accepted but don't know what exactly the accepted value is. So they might send different decision value and break this protocol. You can see test case about it in the lab, If you don't record accepted value you won't pass the lab. 【在 hyx2011 的大作中提到: 】 : But I don't think proposer need to update its n and v. The accepted number and value seems useless for proposer

shixiaotian机器人#8 · 2015/9/26

你这个只能保证在一次成功的情况下可用啊，如果都不过半数怎么办呢…… 【在 hyx2011 的大作中提到: 】 : 但是就算不发给proposer，提出最大值的proposer在收到大部分acceptor的prepare_ok之后也会发送accept给acceptor，协议也可以完成。发给proposer会让获得返回值的proposer发送重复的消息给acceptor，这不会浪费网络IO么？

shixiaotian机器人#9 · 2015/9/26

随便找本书看卡就行了，细节我也搞不懂，没写过协议…… 【在 aiquestion 的大作中提到: 】 : Orz。。。有啥相关推荐读物或视频么？