Hi Jared,
Thank you. The problem is exactly as you explain below. After checking if the
parent path e.g. job_id exists first, then the problem goes away.
Thanks for your help.
--- On Tue, 9/11/10, Jared Cantwell <jared.cantw...@gmail.com> wrote:
> From: Jared Cantwell <jared.cantw...@gmail.com>
> Subject: Re: Wacther question
> To: zookeeper-user@hadoop.apache.org
> Date: Tuesday, 9 November, 2010, 20:18
> Neo,
>
> To me it looks like this exception is while you are trying
> to call:
>
> zk.create(path, null, Ids.OPEN_ACL_UNSAFE,
> CreateMode.PERSISTENT);
>
> where:
>
> path = "/job_id/task_id/"
>
> Does the node /job_id already exist when you are making
> this request?
> Zookeeper does not recursively create the path you specify,
> only the
> leaf node. If a parent in the path does not
> exist, you can get this
> exception I believe.
>
> As for your concern about the ordering of calling create
> and exist,
> have you tried something like this:
>
> if(zk.exists(path, watcher))
> // start cleaning data in hdfs
>
> If the watcher isn't going to get called (because the node
> already
> exists), you can take action immediately rather than in the
> watcher
> callback...
>
> ~Jared
>
>
> On Sat, Nov 6, 2010 at 7:50 AM, Neo Anderson
> <javadeveloper...@yahoo.co.uk>
> wrote:
> > My question is - what is the right way to received
> notification once a znode is created?
> >
> > My scenario is that I have two threads, one (thread A)
> is going to save data to hdfs, another thread (thread B) is
> going to delete data stored in hdfs once thread A finishes
> its procedure. Thread A will create a znode and Thread B
> uses zk.exists() to register a watch.
> >
> > Thread A will only do
> >
> > zk.create(path, null, Ids.OPEN_ACL_UNSAFE,
> CreateMode.PERSISTENT);
> >
> > at the end (in the final block) of a clean function.
> >
> >
> > The watcher in therad B
> >
> > Watcher watcher = new Watcher(){
> > public void process(WatchedEvent e){
> > boolean exist =
> e.getType().equals(EventType.NodeCreated);
> > boolean path =
> e.getPath().equals("/"+job_id+"/"+task_id);
> > if(exist && path){
> > // start cleaning data in hdfs
> > }
> > }
> >
> > and
> >
> > pass watcher to zk.exists(path, watcher);
> >
> > but I gets `KeeperErrorCode = NoNode for' exception
> >
> > org.apache.zookeeper.KeeperException$NoNodeException:
> KeeperErrorCode = NoNode for /job_id/task_id
> > at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:102)
> > at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:42)
> > at
> org.apache.zookeeper.ZooKeeper.create(ZooKeeper.java:637)
> >
> > It looks like znode doesn't exists because thread A
> still not yet create znode with path '/job_id/task_id';
> however, if I switch to make thread A create znode first
> then therad B executes zk.exists(path, watcher). Problems
> becomes thread B (or its watcher) would never get triggered
> deleting data in hdfs.
> >
> > How to fix this?
> >
> > I appreciate any suggestion.
> >
> > Thanks.
> >
> >
> >
> >
> >
> >
> >
> >
>
