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From Ibrahim <i.s.el-san...@newcastle.ac.uk>
Subject RE: Question about the two-phrase commit
Date Wed, 07 Jan 2015 00:38:22 GMT
Thank you Alexander. I get it

Ibrahim

From: Alexander Shraer-2 [via zookeeper-user] [mailto:ml-node+s578899n7580745h19@n2.nabble.com]
Sent: Wednesday, January 07, 2015 12:29 ص
To: Ibrahim El-sanosi (PGR)
Subject: Re: Question about the two-phrase commit

Edward is totally right - if the operation hasn't been acked by a quorum
then whether or not it is lost depends on failures (both server failures
and network failures) as well as latencies.

The leader doesn't have to re-broadcast everything - when a follower
connects to a leader it tells him whats the last operation in its log and
the leader only needs to send the missing log suffix or a snapshot + suffix
if the follower is really behind.

The leader indeed doesn't know which operations were acked by a quorum. The
operations that weren't acked are always some suffix of the log
(potentially empty).

On Tue, Jan 6, 2015 at 4:19 PM, Ibrahim <[hidden email]</user/SendEmail.jtp?type=node&node=7580745&i=0>>
wrote:

> Thank you Edward for replaying.
>
> In my opinion, your first case can’t happen, because the election
> mechanism will elect the node that has the latest transaction  (zxid) seen.
> In this case, it will be only your second case is correct, unless the node
> that has latest transaction crashes forever.
>
> Ibrahim
> From: Edward Carter [via zookeeper-user] [mailto:
> [hidden email]</user/SendEmail.jtp?type=node&node=7580745&i=1>]
> Sent: Tuesday, January 06, 2015 11:53 م
> To: Ibrahim El-sanosi (PGR)
> Subject: Re: Question about the two-phrase commit
>
> If an operation is logged to disk on a minority of servers, then what
> happens on restart depends on which server wins the leader election.  Since
> the new operation is on a minority, depending on network conditions, a
> server that did *not* log the operation might win the leader election.  In
> this case, the operation will be discarded.  If a server that *did* log the
> operation wins the leader election (as would be the case in the absence of
> network or latency issues), then the operation will be propagated to the
> remaining servers in the ensemble.
>
> Edward
>
> On Jan 6, 2015, at 3:42 PM, Ibrahim <[hidden
> email]</user/SendEmail.jtp?type=node&node=7580741&i=0>> wrote:
>
> > Hi Alexander,
> >
> > So, you meant that if there is operation loged to the disk but it hasn't
> got
> > enough majority, then if the zookeeper servers restart, the new leader
> will
> > re-broadcast the loged operation again to the followers to commit that
> > operation.
> >
> > Does above what you meant by (NEWLEADER message acts as the accept and
> > UPTODATE message acts as commit).
> >
> > Am I right?
> >
> > Thank you
> >
> > Ibrahim
> >
> >
> >
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