yeah, i was thinking it should be in forrest, but i couldn't figure out where to put it. that is why i didn't close the issue.
ben -----Original Message----- From: Patrick Hunt [mailto:ph...@apache.org] Sent: Friday, January 09, 2009 9:37 AM To: zookeeper-user@hadoop.apache.org Subject: Re: Updated NodeWatcher... Ben this is great, thanks! Do you want to close out this one and point to the faq? https://issues.apache.org/jira/browse/ZOOKEEPER-264 Although IMO this should be moved to the forrest docs. Patrick Benjamin Reed wrote: > I'm really bad a creating figures, but i've put up something that should be > informative. (i'm also really bad at apache wiki.) hopefully someone can make > it more beautiful. i've added the state diagram to the FAQ: > http://wiki.apache.org/hadoop/ZooKeeper/FAQ > > ben > > -----Original Message----- > From: adam.ros...@gmail.com [mailto:adam.ros...@gmail.com] On Behalf Of Adam > Rosien > Sent: Thursday, January 08, 2009 8:06 PM > To: zookeeper-user@hadoop.apache.org > Subject: Re: Updated NodeWatcher... > > It feels like we need a flowchart, state-chart, or something, so we > can all talk about the same thing. Then people could suggest > abstractions that would essentially put a box around sections of the > diagram. However I feel woefully inadequate at the former :(. > > .. Adam > > On Thu, Jan 8, 2009 at 4:20 PM, Benjamin Reed <br...@yahoo-inc.com> wrote: >> For your first issue if an ensemble goes offline and comes back, everything >> should be fine. it will look to the client just like a server went down. if >> a session expires, you are correct that the client will not reconnect. this >> again is on purpose. for the node watcher the session is unimportant, but if >> the ZooKeeper object is also being used for leader election, for example, >> you do not want the object to grab a new session automatically. >> >> For 2) i think pat responded to that one. an async request will always >> return. if the server goes down after the request is issued, you will get a >> connection loss error in your callback. >> >> Your third issued is described with the first. >> >> ben >> >> -----Original Message----- >> From: burtona...@gmail.com [mailto:burtona...@gmail.com] On Behalf Of Kevin >> Burton >> Sent: Thursday, January 08, 2009 4:02 PM >> To: zookeeper-user@hadoop.apache.org >> Subject: Re: Updated NodeWatcher... >> >>> >>> i just found that part of this thread went to my junk folder. can you send >>> the URL for the NodeListener? >>> >> Sure... here you go: >> >> http://pastebin.com/f1e9d3706 >> >> >>> this NodeWatcher is a useful thing. i have a couple of suggestions to >>> simplify it: >>> >>> 1) Construct the NodeWatcher with a ZooKeeper object rather than >>> constructing one. Not only does it simplify NodeWatcher, but it also makes >>> it so that the ZooKeeper object can be used for other things as well. >> >> I hear you.... I was thinking that this might not be a good idea because >> NodeWatcher can reconnect you to the ensemble if it goes offline. >> >> I'm not sure if it's a bug or not but once my session expired on the client >> it wouldn't reconnect so I just implemented my own reconnect and session >> expiry. >> >> >>> 2) Use the async API in watchNodeData and watchNodeExists. it simplifies >>> the code and the error handling. >> >> The problem was that according to feedback here an async request might never >> return if the server dies shortly after the request and before it has a >> change to respond. >> >> I wanted NodeWatcher to hide as much rope as possible. >> >> >>> 3) You don't need to do a connect() in handleDisconnected(). ZooKeeper >>> object will do it automatically for you. >>> >>> >> I can try again if you'd like by this isn't my experience. Once the session >> expired and the whole ensemble was offline it wouldn't connect again. >> >> If it was a transient disconnect I'd see on disconnect event and then a >> quick reconnect. If it was a long disconnect (with nothing to attach to) >> then ZK won't ever reconnect me. >> >> I'd like this to be the behavior though... >> >> >>> There is an old example on sourceforge >>> http://zookeeper.wiki.sourceforge.net/ZooKeeperJavaExample that may give >>> you some more ideas on how to simplify your code. >>> >> That would be nice.... simple is good! >> >> Kevin >> >> >> -- >> Founder/CEO Spinn3r.com >> Location: San Francisco, CA >> AIM/YIM: sfburtonator >> Skype: burtonator >> Work: http://spinn3r.com >>
