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From Patrick Hunt <ph...@apache.org>
Subject Re: feedback zkclient
Date Thu, 01 Oct 2009 06:57:51 GMT
I started looking a bit more closely at the source, some questions:

1) I tried generating the javadocs (see my fork of the project on github 
if you want my changes to build.xml for this) but it looks like there's 
pretty much no javadoc. Some information, particularly on semantics of 
user-exposed operations would be useful (esp re my earlier README 
comment - some high level document describing the benefits, etc... of 
the library)

If I'm your proto-typical "lazy developer" (which I am :-) ), I'm really 
expecting some helpful docs to get me bootstrapped.

2) what purpose does ZkEventThread serve?

3) there's definitely an issue in the retryUntilConnected logic that you 
need to address

let's say you call zkclient.create, and the connection to the server is 
lost while the request is in flight. At this point ConnectionLoss is 
thrown on the client side, however you (client) have no information on 
whether the server has made the change or not. The retry method's while 
loop will re-run the create (after reconnect), and the result seen by 
the caller (user code) could be either OK or may be NODEEXISTS 
exception, there's no way to know which.

Mahadev is working on ZOOKEEPER-22 which will address this issue, but 
that's a future version, not today.

4) when I saw that you had separated zkclient and zkconnection I thought 
"ah, this is interesting" however when I saw the implementation I was 

a) what purpose does this separation serve?
b) I thought it was to allow multiple zkclients to share a single 
connection, however looking at zkclient.close, it closes the underlying 

5) there's a lot of wrapping of exceptions, looks like this is done in 
order to make them unchecked. Is this wise? How much "simpler" does it 
really make things? Esp things like interrupted exception? As you 
mentioned, one of your intents is to simplify things, but perhaps too 
simple? Some short, clear examples of usage would be helpful here to 
compare/contrast, I took a very quick look at some of the tests but that 
didn't help much. Is there a test(s) in particular that I should look at 
to see how zkclient is used, and the benefits incurred?



Patrick Hunt wrote:
> Hi Stefan, two suggestions off the bat:
> 1) fill in something in the README, doesn't have to be final or 
> polished, but give some insight into the what/why/how/where/goals/etc... 
> to get things moving quickly for reviewers & new users.
> 2) you should really discuss on the dev list. It's up to you to include 
> user, but apache discourages use of user for development discussion 
> (plus you'll pickup more developer insight there)
> Patrick
> Stefan Groschupf wrote:
>> Hi Zookeeper developer,
>> it would be great if you guys could give us some feedback about our 
>> project zkclient.
>> http://github.com/joa23/zkclient
>> The main idea is making the life of lazy developers that only want 
>> minimal zk functionality much easier.
>> We have a functionality like zkclient mock making testing easy and 
>> fast without running a real zkserver, simple call back interfaces for 
>> the different event types, reconnecting handling in case of timeout etc.
>> We feel we come closer to a release so it would be great if some 
>> experts could have a look and give us some feedback.
>> Thanks,
>> Stefan
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Hadoop training and consulting
>> http://www.scaleunlimited.com
>> http://www.101tec.com

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