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Zookeeper, mail # dev - Where are we in ZOOKEEPER-1416


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陈迪豪 2014-01-17, 03:12
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Flavio Junqueira 2014-01-17, 12:12
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陈迪豪 2014-01-17, 13:02
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FPJ 2014-01-17, 13:18
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kishore g 2014-01-17, 16:05
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FPJ 2014-01-17, 16:15
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kishore g 2014-01-17, 17:13
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Ted Yu 2014-01-17, 17:17
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Flavio Junqueira 2014-01-17, 19:17
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Ted Yu 2014-01-17, 19:25
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Ted Yu 2014-01-17, 20:34
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Re: Where are we in ZOOKEEPER-1416
kishore g 2014-01-17, 22:10
I think its not a good idea to depend precise deltas, it is very difficult
to program correctly and handle all corner cases. For example, what happens
if the hbase master fails and by the time stand by becomes master there
were other changes on ZK. The new Master will miss the changes that
happened.

Probably a better approach is to always depend on the snapshot of the
cluster state. The function that handles any event should be idempotent
given the state of the cluster.
On Fri, Jan 17, 2014 at 12:34 PM, Ted Yu <[EMAIL PROTECTED]> wrote:

> HBASE-5487 is also related.
>
> The discussion there is very long. Below is an excerpt from Honghua:
>
> too many tricky scenarios/bugs due to ZK watch is one-time(which can result
> in missed state transition) and the notification/process is
> asyncronous(which can lead to delayed/non-update-to-date state in master
> memory).
>
> Cheers
>
>
> On Fri, Jan 17, 2014 at 11:25 AM, Ted Yu <[EMAIL PROTECTED]> wrote:
>
> > Hi, Flavio:
> > HBASE-8365 is one such case.
> >
> > Let me search around for other related discussion.
> >
> >
> > On Fri, Jan 17, 2014 at 11:17 AM, Flavio Junqueira <
> [EMAIL PROTECTED]>wrote:
> >
> >> Hi Ted,
> >>
> >> Can you provide more detail on how the precise deltas could make it more
> >> robust?
> >>
> >> -Flavio
> >>
> >> -----Original Message-----
> >> From: "Ted Yu" <[EMAIL PROTECTED]>
> >> Sent: 17/01/2014 17:25
> >> To: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>
> >> Subject: Re: Where are we in ZOOKEEPER-1416
> >>
> >> Having the ability to know exact deltas would help make HBase region
> >> assignment more robust.
> >>
> >> Cheers
> >>
> >>
> >>
> >> On Fri, Jan 17, 2014 at 9:13 AM, kishore g <[EMAIL PROTECTED]> wrote:
> >>
> >> > I agree with you, I like the side effect and in fact I would prefer to
> >> have
> >> > one notification for all changes under a parent node.
> >> >
> >> > However, Hao is probably asking for ability to know exact deltas.
> >> >
> >> >
> >> > On Fri, Jan 17, 2014 at 8:15 AM, FPJ <[EMAIL PROTECTED]> wrote:
> >> >
> >> > > We don't need to have a mapping between every change and a
> >> notification.
> >> > If
> >> > > there are 2+ changes between notifications, you'll be able to
> observe
> >> it
> >> > by
> >> > > reading the ZK state. In fact, one nice side-effect is that we
> reduce
> >> the
> >> > > number of notifications when there are many concurrent changes.
> >> > >
> >> > > The only situation I can see it being necessary is the one in which
> we
> >> > need
> >> > > to know precisely the changes and we haven't cached a previous
> >> version of
> >> > > the state.
> >> > >
> >> > > -Flavio
> >> > >
> >> > > > -----Original Message-----
> >> > > > From: kishore g [mailto:[EMAIL PROTECTED]]
> >> > > > Sent: 17 January 2014 16:06
> >> > > > To: [EMAIL PROTECTED]
> >> > > > Subject: Re: Where are we in ZOOKEEPER-1416
> >> > > >
> >> > > > I think Hao is pointing out that there is no way to see every
> change
> >> > > > (delta) that happened to a znode. Consider 2 changes A,B in quick
> >> > > > succession. When client gets notified of A and before setting the
> >> watch
> >> > > the
> >> > > > change B has occurred on the server side. This means the client
> >> cannot
> >> > > know
> >> > > > the delta A. Client can only read the state after change B is
> >> applied.
> >> > > >
> >> > > > Implementing the concept of Persistent watcher guarantees that
> >> client
> >> > if
> >> > > > notified after every change.
> >> > > >
> >> > > > This is a nice to have feature but I dont understand the
> >> requirement in
> >> > > Hbase
> >> > > > where this is needed. Hao, can you shed more light on how this
> >> would be
> >> > > > useful for HBase (to act like state machine)
> >> > > >
> >> > > > thanks,
> >> > > > Kishore G
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > >
> >> > > > On Fri, Jan 17, 2014 at 5:18 AM, FPJ <[EMAIL PROTECTED]>
> wrote:
> >> > > >
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Ted Dunning 2014-01-17, 22:14
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Ted Dunning 2014-01-17, 22:41
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陈迪豪 2014-01-18, 04:33
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Ted Yu 2014-01-17, 22:54
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Stack 2014-01-18, 16:58
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Ted Dunning 2014-01-19, 00:05
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Ted Yu 2014-01-19, 01:11
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陈迪豪 2014-01-28, 07:02
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Thawan Kooburat 2014-01-28, 05:29
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Thawan Kooburat 2014-01-25, 02:49