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RE: Where are we in ZOOKEEPER-1416
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:
> > >
> > > > But you don't really miss events, you'll see them when you read the
> ZK
> > > > state. If you follow the pattern I described, you're supposed to
> > > > observe all changes. Perhaps I'm missing some concrete use case you
> > > > have mind.
> > > >
> > > > -Flavio
> > > >
> > > > > -----Original Message-----
> > > > > From: 陈迪豪 [mailto:[EMAIL PROTECTED]]
> > > > > Sent: 17 January 2014 13:03
> > > > > To: [EMAIL PROTECTED]
> > > > > Subject: RE: Where are we in ZOOKEEPER-1416
> > > > >
> > > > > No, it's not complicated. But for the people who don't understand
> zk
> > > > deeply,
> > > > > they would easily ignore the fact that they would miss events in
> > > > > some
> > > > way.
> > > > > Moreover, I think providing persistent watch is good for developers
> > > > > to
> > > > build
> > > > > the "state-machine" application. Actually, HBase suffer from
> missing
> > > > > the intermediate state when use zk to store the data.
> > > > >
> > > > > If the feature is implemented, I would like to see the patch and
> > > > > consider
> > > > if it
> > > > > can be used for us.
> > > > >
> > > > > ________________________________________
> > > > > From: Flavio Junqueira [[EMAIL PROTECTED]]
> > > > > Sent: Friday, January 17, 2014 8:12 PM
> > > > > To: [EMAIL PROTECTED]
> > > > > Subject: RE: Where are we in ZOOKEEPER-1416
> > > > >
> > > > > My take is that persistent subscriptions add complexity and are not
> > > > strictly
> > > > > necessary. You can follow this pattern of setting a watch, reading
> > > > > the
> > > > state
> > > > > upon a notification and setting a new watch. Why do you feel that's