Re: [Zookeeper-user] [Bug?] Notification not guaranteed

[Benjamin R. <br...@ya...>]

We call permantent watches subscriptions see 
(http://zookeeper.wiki.sourceforge.net/SubscribeMethod). I really want to do 
it and I think it would be very useful and more than a convenience it 
actually provides more functionality. Unfortunately, we just don't have the 
bandwidth right now to implement it. The fortunate thing is that it is "just 
a matter of programming" all the information is there and all the needed 
information is already being replicated and saved in the transaction log.

ben

On Friday 25 April 2008 10:01:40 Bartlomiej Niechwiej wrote:
> Ben,
>
> I think the best approach would be to support permanent watches, a
> feature which has been asked for since the very beginning...
>
> Not only would it cease the endless discussion of naming, but it would
> also provide a powerful feature ;-)
>
> Just a thought ;-)
>
> B.
>
> -----Original Message-----
> From: zoo...@li...
> [mailto:zoo...@li...] On Behalf Of
> Benjamin Reed
> Sent: Friday, April 25, 2008 8:48 AM
> To: zoo...@li...
> Subject: Re: [Zookeeper-user] [Bug?] Notification not guaranteed
>
> Naming and the semantics it implies can be an endless argument. Unless
> we call
> it a one time trigger I think people will think of SQL triggers which
> are not
> one time. (I'm not saying that watch is any better.)
>
> I agree about the java doc clarifications. I've been working on it since
> Ted
> brought it up, but I've been side tracked by the session loss bug. I'm
> hoping
> to finish up today. I'll make sure the javadoc emphasizes the way
> watches
> work.
>
> ben
>
> On Friday 25 April 2008 00:14:11 Patrick Hunt wrote:
> > Benjamin Reed wrote:
> > > This is really a key point for new users to understand, so any
>
> pointers
>
> > > on how we can clarify that page would be very helpful!
> >
> > Part of the issue may be the naming itself. For whatever reason I
> > associate "watch" with something long lived - not a "one time
> > notification" which I would associate more naturally with "trigger".
> >
> > I jumped in right way and started using the java client/server. The
>
> java
>
> > client javadoc in particular is not clear about watches being "one
>
> time
>
> > notifications". Would def help to fix the javadoc on this point.
> >
> > Patrick
> >
> > > ----- Original Message ----
> > > From: Stefan Groschupf <sg...@10...>
> > > To: zoo...@li...
> > > Sent: Thursday, April 24, 2008 10:19:16 PM
> > > Subject: [Zookeeper-user] [Bug?] Notification not guaranteed
> > >
> > > Hi there,
> > > as far I understand notification is guaranteed for e.g. child
>
> creation.
>
> > > However I have a test that shows that randomly I do not get all
> > > notification I do expect.
> > > I basically create 10 child in /folder but only get 8 or 9
> > > notifications back.
> > > However in case I add a Thread.sleep(50); between my child znode
> > > creation I always get 10 notifications.
> > >
> > > Is that a bug or an optimization, e.g. getting one notification for
> > > two new sub znode creations?
> > > Thanks for any hints.
> > > Stefan
> > >
> > > My code looks like this:
> > >
> > > TestMethod:
> > >
> > >   public void testNotifications() throws Exception {
> > >          KattaConfiguration conf = new KattaConfiguration();
> > >          Server server = new Server(conf);
> > >          ZKClient client = new ZKClient(conf);
> > >          MyListener listener = new MyListener();
> > >          String katta = "/katta";
> > >          if (client.exists(katta)) {
> > >              client.deleteRecursiv(katta);
> > >          }
> > >          client.create(katta);
> > >          client.subscribeChildChanges(katta, listener);
> > >          for (int i = 0; i < 10; i++) {
> > >              client.create(katta + "/" + i);
> > > //            Thread.sleep(50);
> > >          }
> > >          Thread.sleep(1000);
> > >          assertEquals(10, listener._counter);
> > >          server.shutdown();
> > >      }
> > >
> > > Watcher process Method:
> > >
> > >      public void process(WatcherEvent event) {
> > >          synchronized (_mutex) {
> > >              String path = event.getPath();
> > >               if (event.getType() ==
> > > Watcher.Event.EventNodeChildrenChanged) {
> > >                  HashSet<IZKEventListener> listeners =
> > > _childListener.get(path);
> > >                  if (listeners != null) {
> > >                      for (IZKEventListener listener : listeners) {
> > >                          listener.process(event);
> > >                      }
> > >                      // re subscribe to event.
> > >                      try {
> > >                          _zk.getChildren(event.getPath(), true);
> > >                      } catch (Exception e) {
> > >                          for (IZKEventListener listener : listeners)
>
> {
>
> > >                              removeListener(path, listener);
> > >                          }
> > >                          Logger.warn("unable to re subscribe to
>
> child
>
> > > change notification", e);
> > >                      }
> > >                  }
> > >              }
> > >          }
> > >      }
> > >
> > >
> > >
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > 101tec Inc.
> > > Menlo Park, California, USA
> > > http://www.101tec.com
>
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