zookeeper-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From daidong <daidon...@gmail.com>
Subject Re: Problems about Zab protocol
Date Thu, 21 Apr 2011 06:33:20 GMT
Thanks for this paper info... It is formalized and not easy to understand. 

Still reading... :P

-- 
daidong
Sent with Sparrow
On 2011年4月21日星期四 at 上午7:21, André Oriani [via zookeeper-user] wrote: 
>  If you wanna go deep on Zab http://research.yahoo.com/files/YL-2010-007.pdf
> 
> - 
> André 
> 
> On Wed, Apr 20, 2011 at 17:26, Benjamin Reed <[hidden email]> 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. 
> >> 
> > 
> 
> 
> If you reply to this email, your message will be added to the discussion below: http://zookeeper-user.578899.n2.nabble.com/Problems-about-Zab-protocol-tp6290102p6292678.html

>  To unsubscribe from Problems about Zab protocol, click here. 
> 
> 
> 



--
View this message in context: http://zookeeper-user.578899.n2.nabble.com/Problems-about-Zab-protocol-tp6290102p6293373.html
Sent from the zookeeper-user mailing list archive at Nabble.com.
Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message