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From daidong <daidon...@gmail.com>
Subject Re: Problems about Zab protocol
Date Thu, 21 Apr 2011 06:35:51 GMT
This is the idea i can not get :)

Why do not have aborts can simplify 2PC without any affects on Integrity?

Thanks!
-- 
daidong
Sent with Sparrow
On 2011年4月21日星期四 at 上午4:26, Benjamin Reed-3 [via zookeeper-user] wrote: 
>  just to add a bit to alex's reponse: we do a simplified 2pc since we 
> do not have aborts. we also differ from 2pc during recovery which is 
> made up of two sub phases. 
> 
> ben 
> 
> On Wed, Apr 20, 2011 at 11:29 AM, Alexander Shraer 
> <[hidden email]> wrote: 
> 
> > Hi, 
> > 
> > Regarding your first question - ZAB has two parts - the broadcast protocol you mention,

> > which is executed by a leader, and the leader election protocol, which recovers
from a leader failure. 
> > This is similar to the way other state-machine replication algorithms work, where
you have 
> > a fast normal mode and a slower recovery mode (you don't need to execute both all
the time - only when the leader fails). 
> > See Paxos state-machine replication for example (section 3): http://research.microsoft.com/en-us/um/people/lamport/pubs/pubs.html#paxos-simple
> > 
> > Regarding your second question - Zookeeper basically guarantees so called "sequential
consistency" semantics. 
> > This guarantees that the real execution looks to clients like some sequential execution
in which 
> > the operations of every client appear in the order they were submitted. It does
not guarantee that a read of one client 
> > returns the latest value written by another client. This allows reads to be executed
locally. If you need to return the latest 
> > state, you can use the sync() call which flushes the pending updates between the
leader and a follower. 
> > See also the "consistency guarantees" section here: 
> > http://hadoop.apache.org/zookeeper/docs/r3.3.1/zookeeperProgrammers.html
> > 
> > Alex 
> > 
> >> -----Original Message----- 
> >> From: daidong [mailto:[hidden email]] 
> >> Sent: Wednesday, April 20, 2011 2:38 AM 
> >> To: [hidden email] 
> >> Subject: Problems about Zab protocol 
> >> 
> >> Hi, everyone. 
> >> 
> >> Recently, i read the paper "a simple total ordered broadcast protocol" 
> >> and 
> >> there are some problems i can not figure out. Hope anyone can help 
> >> me... :P 
> >> 
> >> The paper describes the Zab protocol as a 2 phase commit protocol when 
> >> system is under broadcast mode. However some paper(Skeen 82, "A Quorum 
> >> Based 
> >> Commit Protocol") has mentioned if we want to extend an 2PC to adapt a 
> >> quorum based commit protocol we must introduce a three phase commit 
> >> protocol(In fact, i haven't quit understood this, :( ). However 
> >> according 
> >> Zab paper, this still can be done. Why and how to do this? 
> >> 
> >> Secondly, even Zookeeper can guarantee that status in different 
> >> followers 
> >> are consistent. However, this consistency only works among a quorum of 
> >> followers that has acked the COMMIT. As the client can connect to any 
> >> followers when perform reading action, so what happens if the client 
> >> happens 
> >> to connect with the follower that has not acked the COMMIT? I can not 
> >> find 
> >> the information in this paper... 
> >> 
> >> If i ask some naive question, Hope anybody can tell me where i can find 
> >> the 
> >> answer or some suggestions, thanks :) 
> >> 
> >> 
> >> -- 
> >> View this message in context: http://zookeeper-
> >> user.578899.n2.nabble.com/Problems-about-Zab-protocol- 
> >> tp6290102p6290102.html 
> >> Sent from the zookeeper-user mailing list archive at Nabble.com. 
> > 
> 
> 
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> 



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