Mailing-List: contact zookeeper-user-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: zookeeper-user@hadoop.apache.org
Received-SPF: neutral (nike.apache.org: local policy)
DomainKey-Signature: a=rsa-sha1; s=serpent; d=yahoo-inc.com; c=nofws; q=dns;
	h=message-id:date:from:user-agent:mime-version:to:subject:
	references:in-reply-to:content-type:content-transfer-encoding;
	b=Tyr93JXfZnyqOBycrcutB5Fk+Tl6NF5OZUu0ShRj9KlSOjPcV6InSk+58MCly7tS
Message-ID: <4A048F93.1000309@yahoo-inc.com>
Date: Fri, 08 May 2009 13:01:23 -0700
From: Benjamin Reed <breed@yahoo-inc.com>
User-Agent: Thunderbird 2.0.0.21 (X11/20090409)
MIME-Version: 1.0
To: "zookeeper-user@hadoop.apache.org" <zookeeper-user@hadoop.apache.org>
Subject: Re: NodeChildrenChanged WatchedEvent
References: <a94a47380905081211i242d92d6kf1517cb410cc0c3f@mail.gmail.com>
In-Reply-To: <a94a47380905081211i242d92d6kf1517cb410cc0c3f@mail.gmail.com>
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

i'm adding a faq on this right now. it's a rather common request.

we could put in the name of the node that is changing. indeed, we did in 
the first cut of zookeeper, but then we found that every instance of 
programs that used this resulted in bugs, so we removed it.

here is the problem:

you do a getChildren(), an event comes in that "foo" is deleted, and 
right afterwords "goo" gets deleted, but you aren't going to get that 
event since the previous delete fired and you haven't done another 
getChildren(). this almost always results in an error, so much so that 
we don't even give people the rope.

ben

Javier Vegas wrote:
> Hi, I am starting to implement Zookeeper as an arbiter for a high
> performance client-server service, it is working really well but I
> have a question. When my Watcher receives an event of
> NodeChildrenChanged event, is there any way of getting from the event
> the path for the child that changed? The WatchedEvent javadoc says
> that it "includes exactly what happened" but all I am able to extract
> is a vague "NodeChildrenChanged" type. What I am doing now to figure
> out the path of teh new child is to do a new getChildren and compare
> the new children list with the old children list, but that seems a
> waste of time and bandwith if my node has lots of children and is
> watched by a loot of zookeepers (which will be in prod). If I can
> somehow get the path of the added/deleted child from the
> WatchedEvent, it will make my life easier and my Zookeeper-powered
> system much more simple, robust and scalable. Any suggestions?
>
> Thanks,
>
> Javier Vegas
>