High WTF count in ZooKeeper client code

[Thomas Koch <th...@koch.ro>]

Hi,

I started yesterday to work on my idea of an alternative ZooKeeper client 
interface.[1] Instead of methods on a ZooKeeper class, a user should 
instantiate an Operation (Create, Delete, ...) and forward it to an Executor 
which handles session loss errors and alikes.

By doing that, I got shocked by the sheer number of WTF issues I found. I'm 
sorry for ranting now, but it gets quicker to the poing.

- Hostlist as string

The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of 
not doing (too much) work in a ctor. Instead the ClientCnxn should receive an 
object of class "HostSet". HostSet could then be instantiated e.g. with a 
comma separated string.

- cyclic dependency ClientCnxn, ZooKeeper

ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds a 
cyclic dependency graph between both objects. This means, you can't have the 
one without the other. So why did you bother do make them to separate classes 
in the first place?
ClientCnxn accesses ZooKeeper.state. State should rather be a property of 
ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method 
primeConnection(). I've not yet checked, how this dependency should be 
resolved better.

- Chroot is an attribute of ClientCnxn

I'd like to have one process that uses ZooKeeper for different things 
(managing a list of work, locking some unrelated locks elsewhere). So I've 
components that do this work inside the same process. These components should 
get the same zookeeper-client reference chroot'ed for their needs.
So it'd be much better, if the ClientCnxn would not care about the chroot.

- deleteRecursive does not belong to the other methods

DeleteRecursive has been committed to trunk already as a method to the 
zookeeper class. So in the API it has the same level as the atomic operations 
create, delete, getData, setData, etc. The user must get the false impression, 
that deleteRecursive is also an atomic operation.
It would be better to have deleteRecursive in some helper class but not that 
deep in zookeeper's core code. Maybe I'd like to have another policy on how to 
react if deleteRecursive fails in the middle of its work?

- massive code duplication in zookeeper class

Each operation calls validatePath, handles the chroot, calls ClientCnxn and 
checks the return header for error. I'd like to address this with the 
operation classes:
Each operation should receive a prechecked Path object. Calling ClientCnxn and 
error checking is not (or only partly) the concern of the operation but of an 
"executor" like class.

- stat is returned by parameter

Since one can return only one value in java it's the only choice to do so. 
Still it feels more like C then like Java. However with operator classes one 
could simply get the result values with getter functions after the execution.

- stat calls static method on org.apache.zookeeper.server.DataTree

It's a huge jump from client code to the internal server class DataTree. 
Shouldn't there rather be some class related to the protobuffer stat class 
that knows how to copy a stat?

- Session class?

Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and 
sessionTimeout in a Session class so that the ctor of ClientCnxn won't get too 
long?

I may have missed some items. :-)

Once again, please excuse my harsh tone. May I put the above issues in jira 
and would you accept (backwards compatible) patches for it for 3.4.0?

Zookeeper is a fascinating project. Cudos to the devs. I've only looked in the 
client side code, which is what most users of zookeeper will ever see if they 
see any zookeeper internal code at all. So it may make sense to make this 
piece of the project as nice and clean as possible.

[1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E

Best regards,

Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Patrick Hunt <ph...@apache.org>]

Hi Thomas, thanks for the reports, esp the JIRAs. One you missed (and 
aptly numbered) that's a pet peeve of mine is this one:

https://issues.apache.org/jira/browse/ZOOKEEPER-666

I think part of what you are seeing is that the C api matured more 
quickly, and directly influenced the development of the java api. Given 
that the team is resource constrained we tend to prioritize fixes & 
stability over code cleanup. Mahadev and I often talk about addressing 
these (and the server has some of this as well, esp given it's relative 
size) but more pressing issues keep us from getting to it.

You seem pretty fired up to address these, I look forward to seeing some 
patches. Anyone can become a contributor, you'll find our "how to 
contribute" docs here:
http://wiki.apache.org/hadoop/ZooKeeper/HowToContribute

Regards,

Patrick

On 08/11/2010 02:45 AM, Thomas Koch wrote:
> Hi,
>
> I started yesterday to work on my idea of an alternative ZooKeeper client
> interface.[1] Instead of methods on a ZooKeeper class, a user should
> instantiate an Operation (Create, Delete, ...) and forward it to an Executor
> which handles session loss errors and alikes.
>
> By doing that, I got shocked by the sheer number of WTF issues I found. I'm
> sorry for ranting now, but it gets quicker to the poing.
>
> - Hostlist as string
>
> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
> not doing (too much) work in a ctor. Instead the ClientCnxn should receive an
> object of class "HostSet". HostSet could then be instantiated e.g. with a
> comma separated string.
>
> - cyclic dependency ClientCnxn, ZooKeeper
>
> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds a
> cyclic dependency graph between both objects. This means, you can't have the
> one without the other. So why did you bother do make them to separate classes
> in the first place?
> ClientCnxn accesses ZooKeeper.state. State should rather be a property of
> ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
> primeConnection(). I've not yet checked, how this dependency should be
> resolved better.
>
> - Chroot is an attribute of ClientCnxn
>
> I'd like to have one process that uses ZooKeeper for different things
> (managing a list of work, locking some unrelated locks elsewhere). So I've
> components that do this work inside the same process. These components should
> get the same zookeeper-client reference chroot'ed for their needs.
> So it'd be much better, if the ClientCnxn would not care about the chroot.
>
> - deleteRecursive does not belong to the other methods
>
> DeleteRecursive has been committed to trunk already as a method to the
> zookeeper class. So in the API it has the same level as the atomic operations
> create, delete, getData, setData, etc. The user must get the false impression,
> that deleteRecursive is also an atomic operation.
> It would be better to have deleteRecursive in some helper class but not that
> deep in zookeeper's core code. Maybe I'd like to have another policy on how to
> react if deleteRecursive fails in the middle of its work?
>
> - massive code duplication in zookeeper class
>
> Each operation calls validatePath, handles the chroot, calls ClientCnxn and
> checks the return header for error. I'd like to address this with the
> operation classes:
> Each operation should receive a prechecked Path object. Calling ClientCnxn and
> error checking is not (or only partly) the concern of the operation but of an
> "executor" like class.
>
> - stat is returned by parameter
>
> Since one can return only one value in java it's the only choice to do so.
> Still it feels more like C then like Java. However with operator classes one
> could simply get the result values with getter functions after the execution.
>
> - stat calls static method on org.apache.zookeeper.server.DataTree
>
> It's a huge jump from client code to the internal server class DataTree.
> Shouldn't there rather be some class related to the protobuffer stat class
> that knows how to copy a stat?
>
> - Session class?
>
> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
> sessionTimeout in a Session class so that the ctor of ClientCnxn won't get too
> long?
>
> I may have missed some items. :-)
>
> Once again, please excuse my harsh tone. May I put the above issues in jira
> and would you accept (backwards compatible) patches for it for 3.4.0?
>
> Zookeeper is a fascinating project. Cudos to the devs. I've only looked in the
> client side code, which is what most users of zookeeper will ever see if they
> see any zookeeper internal code at all. So it may make sense to make this
> piece of the project as nice and clean as possible.
>
> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
>
> Best regards,
>
> Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Patrick Hunt <ph...@apache.org>]

However it should be pretty easy to apply though given our stability and
relatively small size. :-) Seems like it would be useful for users and
developers both...

Patrick

On Fri, Sep 3, 2010 at 11:49 PM, Mahadev Konar <ma...@yahoo-inc.com>wrote:

> I was able to get hold of one of the hadoop developers. So the gist of the
> story is,
>
> They have interface tagging saying
>
> Something like
>
> @Audience.limitedPrivate(target="pig")
>
> Wherin this interface is defined for pig and is only to be used by pig
> oflks.
>
> Interfaces can be defined as public, stable, unstable, ......
>
> This is quite useful but given out interfaces havent chanhged in a long
> time
> this might not be that helpful for us.
>
> Thanks
> mahadev
>
>
> On 8/31/10 3:47 PM, "Mahadev Konar" <ma...@yahoo-inc.com> wrote:
>
> > There isnt any documentation on the interface tagging other than the
> running
> > comments. I will try to get hold of one of the hadoop folks to get me a
> dump
> > of the info and will create a jira!
> >
> > Thanks
> > mahadev
> >
> >
> > On 8/11/10 9:56 AM, "Patrick Hunt" <ph...@apache.org> wrote:
> >
> > wrt defining interface stability we should adopt something like hadoop
> > is now doing:
> >
> > https://issues.apache.org/jira/browse/HADOOP-5073
> >
> > Mahadev, do you know if this is documented somewhere? "final"
> > documentation, rather than the running commentary thats on this jira? We
> > could adopt something similar/same. Can you create a jira for that?
> >
> > Patrick
> >
> > On 08/11/2010 08:23 AM, Thomas Koch wrote:
> >> Hallo Mahadev,
> >>
> >> thank you for your nice answer. Yes, we'll of cause preserve
> compatibility.
> >> Otherwise there is no chance to get accepted.
> >>
> >> I assume the following things must keep their interfaces:
> >> ZooKeeper (It'll call the new interface in the background),
> ASyncCallback,
> >> Watcher
> >> We may want to change: ClientCnxn (faktor out some things, remove dep on
> >> ZooKeeper)
> >>
> >> I think other classes should not be involved at all in our issues. My
> >> collegue
> >> Patrick was so kind to fill the jira issues.
> >>
> >> Best regards,
> >>
> >> Thomas
> >>
> >>
> >> Mahadev Konar:
> >>> Also, I am assuming you have backwards compatability in mind when you
> >>> suggest these changes right?
> >>>
> >>> The interfaces of zookeeper client should not be changing as part of
> this,
> >>> though the recursive delete hasn't been introduced yet (its only
> available
> >>> in 3.4, so we can move it out into a helper class).
> >>>
> >>> Thanks
> >>> mahadev
> >>>
> >>>
> >>> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>  wrote:
> >>>
> >>> HI Thomas,
> >>>    I read through the list of issues you posted, most of them seem
> >>> reasonable to fix. The one's you have mentioned below might take quite
> a
> >>> bit of time to fix and again a lot of testing! (just a warning :)). It
> >>> would be great if you'd want to clean this up for 3.4. Please go ahead
> and
> >>> file a jira. These improvements would be good to have in the zookeeper
> >>> java client.
> >>>
> >>> For deleteRecursive, I definitely agree that it should be a helper
> class. I
> >>> don't believe it should be in the direct zookeeper api!
> >>>
> >>> Thanks
> >>> mahadev
> >>>
> >>>
> >>> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>  wrote:
> >>>
> >>> Hi,
> >>>
> >>> I started yesterday to work on my idea of an alternative ZooKeeper
> client
> >>> interface.[1] Instead of methods on a ZooKeeper class, a user should
> >>> instantiate an Operation (Create, Delete, ...) and forward it to an
> >>> Executor which handles session loss errors and alikes.
> >>>
> >>> By doing that, I got shocked by the sheer number of WTF issues I found.
> I'm
> >>> sorry for ranting now, but it gets quicker to the poing.
> >>>
> >>> - Hostlist as string
> >>>
> >>> The hostlist is parsed in the ctor of ClientCnxn. This violates the
> rule of
> >>> not doing (too much) work in a ctor. Instead the ClientCnxn should
> receive
> >>> an object of class "HostSet". HostSet could then be instantiated e.g.
> with
> >>> a comma separated string.
> >>>
> >>> - cyclic dependency ClientCnxn, ZooKeeper
> >>>
> >>> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor
> builds
> >>> a cyclic dependency graph between both objects. This means, you can't
> have
> >>> the one without the other. So why did you bother do make them to
> separate
> >>> classes in the first place?
> >>> ClientCnxn accesses ZooKeeper.state. State should rather be a property
> of
> >>> ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its
> method
> >>> primeConnection(). I've not yet checked, how this dependency should be
> >>> resolved better.
> >>>
> >>> - Chroot is an attribute of ClientCnxn
> >>>
> >>> I'd like to have one process that uses ZooKeeper for different things
> >>> (managing a list of work, locking some unrelated locks elsewhere). So
> I've
> >>> components that do this work inside the same process. These components
> >>> should get the same zookeeper-client reference chroot'ed for their
> needs.
> >>> So it'd be much better, if the ClientCnxn would not care about the
> chroot.
> >>>
> >>> - deleteRecursive does not belong to the other methods
> >>>
> >>> DeleteRecursive has been committed to trunk already as a method to the
> >>> zookeeper class. So in the API it has the same level as the atomic
> >>> operations create, delete, getData, setData, etc. The user must get the
> >>> false impression, that deleteRecursive is also an atomic operation.
> >>> It would be better to have deleteRecursive in some helper class but not
> >>> that deep in zookeeper's core code. Maybe I'd like to have another
> policy
> >>> on how to react if deleteRecursive fails in the middle of its work?
> >>>
> >>> - massive code duplication in zookeeper class
> >>>
> >>> Each operation calls validatePath, handles the chroot, calls ClientCnxn
> and
> >>> checks the return header for error. I'd like to address this with the
> >>> operation classes:
> >>> Each operation should receive a prechecked Path object. Calling
> ClientCnxn
> >>> and error checking is not (or only partly) the concern of the operation
> >>> but of an "executor" like class.
> >>>
> >>> - stat is returned by parameter
> >>>
> >>> Since one can return only one value in java it's the only choice to do
> so.
> >>> Still it feels more like C then like Java. However with operator
> classes
> >>> one could simply get the result values with getter functions after the
> >>> execution.
> >>>
> >>> - stat calls static method on org.apache.zookeeper.server.DataTree
> >>>
> >>> It's a huge jump from client code to the internal server class
> DataTree.
> >>> Shouldn't there rather be some class related to the protobuffer stat
> class
> >>> that knows how to copy a stat?
> >>>
> >>> - Session class?
> >>>
> >>> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword
> and
> >>> sessionTimeout in a Session class so that the ctor of ClientCnxn won't
> get
> >>> too long?
> >>>
> >>> I may have missed some items. :-)
> >>>
> >>> Once again, please excuse my harsh tone. May I put the above issues in
> jira
> >>> and would you accept (backwards compatible) patches for it for 3.4.0?
> >>>
> >>> Zookeeper is a fascinating project. Cudos to the devs. I've only looked
> in
> >>> the client side code, which is what most users of zookeeper will ever
> see
> >>> if they see any zookeeper internal code at all. So it may make sense to
> >>> make this piece of the project as nice and clean as possible.
> >>>
> >>> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
> >>> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
> >>>
> >>> Best regards,
> >>>
> >>> Thomas Koch, http://www.koch.ro
> >
> >
>
>

Re: High WTF count in ZooKeeper client code

[Mahadev Konar <ma...@yahoo-inc.com>]

I was able to get hold of one of the hadoop developers. So the gist of the
story is,

They have interface tagging saying

Something like  

@Audience.limitedPrivate(target="pig")

Wherin this interface is defined for pig and is only to be used by pig
oflks. 

Interfaces can be defined as public, stable, unstable, ......

This is quite useful but given out interfaces havent chanhged in a long time
this might not be that helpful for us.

Thanks
mahadev


On 8/31/10 3:47 PM, "Mahadev Konar" <ma...@yahoo-inc.com> wrote:

> There isnt any documentation on the interface tagging other than the running
> comments. I will try to get hold of one of the hadoop folks to get me a dump
> of the info and will create a jira!
> 
> Thanks
> mahadev
> 
> 
> On 8/11/10 9:56 AM, "Patrick Hunt" <ph...@apache.org> wrote:
> 
> wrt defining interface stability we should adopt something like hadoop
> is now doing:
> 
> https://issues.apache.org/jira/browse/HADOOP-5073
> 
> Mahadev, do you know if this is documented somewhere? "final"
> documentation, rather than the running commentary thats on this jira? We
> could adopt something similar/same. Can you create a jira for that?
> 
> Patrick
> 
> On 08/11/2010 08:23 AM, Thomas Koch wrote:
>> Hallo Mahadev,
>> 
>> thank you for your nice answer. Yes, we'll of cause preserve compatibility.
>> Otherwise there is no chance to get accepted.
>> 
>> I assume the following things must keep their interfaces:
>> ZooKeeper (It'll call the new interface in the background), ASyncCallback,
>> Watcher
>> We may want to change: ClientCnxn (faktor out some things, remove dep on
>> ZooKeeper)
>> 
>> I think other classes should not be involved at all in our issues. My
>> collegue
>> Patrick was so kind to fill the jira issues.
>> 
>> Best regards,
>> 
>> Thomas
>> 
>> 
>> Mahadev Konar:
>>> Also, I am assuming you have backwards compatability in mind when you
>>> suggest these changes right?
>>> 
>>> The interfaces of zookeeper client should not be changing as part of this,
>>> though the recursive delete hasn't been introduced yet (its only available
>>> in 3.4, so we can move it out into a helper class).
>>> 
>>> Thanks
>>> mahadev
>>> 
>>> 
>>> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>  wrote:
>>> 
>>> HI Thomas,
>>>    I read through the list of issues you posted, most of them seem
>>> reasonable to fix. The one's you have mentioned below might take quite a
>>> bit of time to fix and again a lot of testing! (just a warning :)). It
>>> would be great if you'd want to clean this up for 3.4. Please go ahead and
>>> file a jira. These improvements would be good to have in the zookeeper
>>> java client.
>>> 
>>> For deleteRecursive, I definitely agree that it should be a helper class. I
>>> don't believe it should be in the direct zookeeper api!
>>> 
>>> Thanks
>>> mahadev
>>> 
>>> 
>>> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>  wrote:
>>> 
>>> Hi,
>>> 
>>> I started yesterday to work on my idea of an alternative ZooKeeper client
>>> interface.[1] Instead of methods on a ZooKeeper class, a user should
>>> instantiate an Operation (Create, Delete, ...) and forward it to an
>>> Executor which handles session loss errors and alikes.
>>> 
>>> By doing that, I got shocked by the sheer number of WTF issues I found. I'm
>>> sorry for ranting now, but it gets quicker to the poing.
>>> 
>>> - Hostlist as string
>>> 
>>> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
>>> not doing (too much) work in a ctor. Instead the ClientCnxn should receive
>>> an object of class "HostSet". HostSet could then be instantiated e.g. with
>>> a comma separated string.
>>> 
>>> - cyclic dependency ClientCnxn, ZooKeeper
>>> 
>>> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds
>>> a cyclic dependency graph between both objects. This means, you can't have
>>> the one without the other. So why did you bother do make them to separate
>>> classes in the first place?
>>> ClientCnxn accesses ZooKeeper.state. State should rather be a property of
>>> ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
>>> primeConnection(). I've not yet checked, how this dependency should be
>>> resolved better.
>>> 
>>> - Chroot is an attribute of ClientCnxn
>>> 
>>> I'd like to have one process that uses ZooKeeper for different things
>>> (managing a list of work, locking some unrelated locks elsewhere). So I've
>>> components that do this work inside the same process. These components
>>> should get the same zookeeper-client reference chroot'ed for their needs.
>>> So it'd be much better, if the ClientCnxn would not care about the chroot.
>>> 
>>> - deleteRecursive does not belong to the other methods
>>> 
>>> DeleteRecursive has been committed to trunk already as a method to the
>>> zookeeper class. So in the API it has the same level as the atomic
>>> operations create, delete, getData, setData, etc. The user must get the
>>> false impression, that deleteRecursive is also an atomic operation.
>>> It would be better to have deleteRecursive in some helper class but not
>>> that deep in zookeeper's core code. Maybe I'd like to have another policy
>>> on how to react if deleteRecursive fails in the middle of its work?
>>> 
>>> - massive code duplication in zookeeper class
>>> 
>>> Each operation calls validatePath, handles the chroot, calls ClientCnxn and
>>> checks the return header for error. I'd like to address this with the
>>> operation classes:
>>> Each operation should receive a prechecked Path object. Calling ClientCnxn
>>> and error checking is not (or only partly) the concern of the operation
>>> but of an "executor" like class.
>>> 
>>> - stat is returned by parameter
>>> 
>>> Since one can return only one value in java it's the only choice to do so.
>>> Still it feels more like C then like Java. However with operator classes
>>> one could simply get the result values with getter functions after the
>>> execution.
>>> 
>>> - stat calls static method on org.apache.zookeeper.server.DataTree
>>> 
>>> It's a huge jump from client code to the internal server class DataTree.
>>> Shouldn't there rather be some class related to the protobuffer stat class
>>> that knows how to copy a stat?
>>> 
>>> - Session class?
>>> 
>>> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
>>> sessionTimeout in a Session class so that the ctor of ClientCnxn won't get
>>> too long?
>>> 
>>> I may have missed some items. :-)
>>> 
>>> Once again, please excuse my harsh tone. May I put the above issues in jira
>>> and would you accept (backwards compatible) patches for it for 3.4.0?
>>> 
>>> Zookeeper is a fascinating project. Cudos to the devs. I've only looked in
>>> the client side code, which is what most users of zookeeper will ever see
>>> if they see any zookeeper internal code at all. So it may make sense to
>>> make this piece of the project as nice and clean as possible.
>>> 
>>> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
>>> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
>>> 
>>> Best regards,
>>> 
>>> Thomas Koch, http://www.koch.ro
> 
> 

Re: High WTF count in ZooKeeper client code

[Mahadev Konar <ma...@yahoo-inc.com>]

There isnt any documentation on the interface tagging other than the running comments. I will try to get hold of one of the hadoop folks to get me a dump of the info and will create a jira!

Thanks
mahadev


On 8/11/10 9:56 AM, "Patrick Hunt" <ph...@apache.org> wrote:

wrt defining interface stability we should adopt something like hadoop
is now doing:

https://issues.apache.org/jira/browse/HADOOP-5073

Mahadev, do you know if this is documented somewhere? "final"
documentation, rather than the running commentary thats on this jira? We
could adopt something similar/same. Can you create a jira for that?

Patrick

On 08/11/2010 08:23 AM, Thomas Koch wrote:
> Hallo Mahadev,
>
> thank you for your nice answer. Yes, we'll of cause preserve compatibility.
> Otherwise there is no chance to get accepted.
>
> I assume the following things must keep their interfaces:
> ZooKeeper (It'll call the new interface in the background), ASyncCallback,
> Watcher
> We may want to change: ClientCnxn (faktor out some things, remove dep on
> ZooKeeper)
>
> I think other classes should not be involved at all in our issues. My collegue
> Patrick was so kind to fill the jira issues.
>
> Best regards,
>
> Thomas
>
>
> Mahadev Konar:
>> Also, I am assuming you have backwards compatability in mind when you
>> suggest these changes right?
>>
>> The interfaces of zookeeper client should not be changing as part of this,
>> though the recursive delete hasn't been introduced yet (its only available
>> in 3.4, so we can move it out into a helper class).
>>
>> Thanks
>> mahadev
>>
>>
>> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>  wrote:
>>
>> HI Thomas,
>>    I read through the list of issues you posted, most of them seem
>> reasonable to fix. The one's you have mentioned below might take quite a
>> bit of time to fix and again a lot of testing! (just a warning :)). It
>> would be great if you'd want to clean this up for 3.4. Please go ahead and
>> file a jira. These improvements would be good to have in the zookeeper
>> java client.
>>
>> For deleteRecursive, I definitely agree that it should be a helper class. I
>> don't believe it should be in the direct zookeeper api!
>>
>> Thanks
>> mahadev
>>
>>
>> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>  wrote:
>>
>> Hi,
>>
>> I started yesterday to work on my idea of an alternative ZooKeeper client
>> interface.[1] Instead of methods on a ZooKeeper class, a user should
>> instantiate an Operation (Create, Delete, ...) and forward it to an
>> Executor which handles session loss errors and alikes.
>>
>> By doing that, I got shocked by the sheer number of WTF issues I found. I'm
>> sorry for ranting now, but it gets quicker to the poing.
>>
>> - Hostlist as string
>>
>> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
>> not doing (too much) work in a ctor. Instead the ClientCnxn should receive
>> an object of class "HostSet". HostSet could then be instantiated e.g. with
>> a comma separated string.
>>
>> - cyclic dependency ClientCnxn, ZooKeeper
>>
>> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds
>> a cyclic dependency graph between both objects. This means, you can't have
>> the one without the other. So why did you bother do make them to separate
>> classes in the first place?
>> ClientCnxn accesses ZooKeeper.state. State should rather be a property of
>> ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
>> primeConnection(). I've not yet checked, how this dependency should be
>> resolved better.
>>
>> - Chroot is an attribute of ClientCnxn
>>
>> I'd like to have one process that uses ZooKeeper for different things
>> (managing a list of work, locking some unrelated locks elsewhere). So I've
>> components that do this work inside the same process. These components
>> should get the same zookeeper-client reference chroot'ed for their needs.
>> So it'd be much better, if the ClientCnxn would not care about the chroot.
>>
>> - deleteRecursive does not belong to the other methods
>>
>> DeleteRecursive has been committed to trunk already as a method to the
>> zookeeper class. So in the API it has the same level as the atomic
>> operations create, delete, getData, setData, etc. The user must get the
>> false impression, that deleteRecursive is also an atomic operation.
>> It would be better to have deleteRecursive in some helper class but not
>> that deep in zookeeper's core code. Maybe I'd like to have another policy
>> on how to react if deleteRecursive fails in the middle of its work?
>>
>> - massive code duplication in zookeeper class
>>
>> Each operation calls validatePath, handles the chroot, calls ClientCnxn and
>> checks the return header for error. I'd like to address this with the
>> operation classes:
>> Each operation should receive a prechecked Path object. Calling ClientCnxn
>> and error checking is not (or only partly) the concern of the operation
>> but of an "executor" like class.
>>
>> - stat is returned by parameter
>>
>> Since one can return only one value in java it's the only choice to do so.
>> Still it feels more like C then like Java. However with operator classes
>> one could simply get the result values with getter functions after the
>> execution.
>>
>> - stat calls static method on org.apache.zookeeper.server.DataTree
>>
>> It's a huge jump from client code to the internal server class DataTree.
>> Shouldn't there rather be some class related to the protobuffer stat class
>> that knows how to copy a stat?
>>
>> - Session class?
>>
>> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
>> sessionTimeout in a Session class so that the ctor of ClientCnxn won't get
>> too long?
>>
>> I may have missed some items. :-)
>>
>> Once again, please excuse my harsh tone. May I put the above issues in jira
>> and would you accept (backwards compatible) patches for it for 3.4.0?
>>
>> Zookeeper is a fascinating project. Cudos to the devs. I've only looked in
>> the client side code, which is what most users of zookeeper will ever see
>> if they see any zookeeper internal code at all. So it may make sense to
>> make this piece of the project as nice and clean as possible.
>>
>> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
>> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
>>
>> Best regards,
>>
>> Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Patrick Hunt <ph...@apache.org>]

wrt defining interface stability we should adopt something like hadoop 
is now doing:

https://issues.apache.org/jira/browse/HADOOP-5073

Mahadev, do you know if this is documented somewhere? "final" 
documentation, rather than the running commentary thats on this jira? We 
could adopt something similar/same. Can you create a jira for that?

Patrick

On 08/11/2010 08:23 AM, Thomas Koch wrote:
> Hallo Mahadev,
>
> thank you for your nice answer. Yes, we'll of cause preserve compatibility.
> Otherwise there is no chance to get accepted.
>
> I assume the following things must keep their interfaces:
> ZooKeeper (It'll call the new interface in the background), ASyncCallback,
> Watcher
> We may want to change: ClientCnxn (faktor out some things, remove dep on
> ZooKeeper)
>
> I think other classes should not be involved at all in our issues. My collegue
> Patrick was so kind to fill the jira issues.
>
> Best regards,
>
> Thomas
>
>
> Mahadev Konar:
>> Also, I am assuming you have backwards compatability in mind when you
>> suggest these changes right?
>>
>> The interfaces of zookeeper client should not be changing as part of this,
>> though the recursive delete hasn't been introduced yet (its only available
>> in 3.4, so we can move it out into a helper class).
>>
>> Thanks
>> mahadev
>>
>>
>> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>  wrote:
>>
>> HI Thomas,
>>    I read through the list of issues you posted, most of them seem
>> reasonable to fix. The one's you have mentioned below might take quite a
>> bit of time to fix and again a lot of testing! (just a warning :)). It
>> would be great if you'd want to clean this up for 3.4. Please go ahead and
>> file a jira. These improvements would be good to have in the zookeeper
>> java client.
>>
>> For deleteRecursive, I definitely agree that it should be a helper class. I
>> don't believe it should be in the direct zookeeper api!
>>
>> Thanks
>> mahadev
>>
>>
>> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>  wrote:
>>
>> Hi,
>>
>> I started yesterday to work on my idea of an alternative ZooKeeper client
>> interface.[1] Instead of methods on a ZooKeeper class, a user should
>> instantiate an Operation (Create, Delete, ...) and forward it to an
>> Executor which handles session loss errors and alikes.
>>
>> By doing that, I got shocked by the sheer number of WTF issues I found. I'm
>> sorry for ranting now, but it gets quicker to the poing.
>>
>> - Hostlist as string
>>
>> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
>> not doing (too much) work in a ctor. Instead the ClientCnxn should receive
>> an object of class "HostSet". HostSet could then be instantiated e.g. with
>> a comma separated string.
>>
>> - cyclic dependency ClientCnxn, ZooKeeper
>>
>> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds
>> a cyclic dependency graph between both objects. This means, you can't have
>> the one without the other. So why did you bother do make them to separate
>> classes in the first place?
>> ClientCnxn accesses ZooKeeper.state. State should rather be a property of
>> ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
>> primeConnection(). I've not yet checked, how this dependency should be
>> resolved better.
>>
>> - Chroot is an attribute of ClientCnxn
>>
>> I'd like to have one process that uses ZooKeeper for different things
>> (managing a list of work, locking some unrelated locks elsewhere). So I've
>> components that do this work inside the same process. These components
>> should get the same zookeeper-client reference chroot'ed for their needs.
>> So it'd be much better, if the ClientCnxn would not care about the chroot.
>>
>> - deleteRecursive does not belong to the other methods
>>
>> DeleteRecursive has been committed to trunk already as a method to the
>> zookeeper class. So in the API it has the same level as the atomic
>> operations create, delete, getData, setData, etc. The user must get the
>> false impression, that deleteRecursive is also an atomic operation.
>> It would be better to have deleteRecursive in some helper class but not
>> that deep in zookeeper's core code. Maybe I'd like to have another policy
>> on how to react if deleteRecursive fails in the middle of its work?
>>
>> - massive code duplication in zookeeper class
>>
>> Each operation calls validatePath, handles the chroot, calls ClientCnxn and
>> checks the return header for error. I'd like to address this with the
>> operation classes:
>> Each operation should receive a prechecked Path object. Calling ClientCnxn
>> and error checking is not (or only partly) the concern of the operation
>> but of an "executor" like class.
>>
>> - stat is returned by parameter
>>
>> Since one can return only one value in java it's the only choice to do so.
>> Still it feels more like C then like Java. However with operator classes
>> one could simply get the result values with getter functions after the
>> execution.
>>
>> - stat calls static method on org.apache.zookeeper.server.DataTree
>>
>> It's a huge jump from client code to the internal server class DataTree.
>> Shouldn't there rather be some class related to the protobuffer stat class
>> that knows how to copy a stat?
>>
>> - Session class?
>>
>> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
>> sessionTimeout in a Session class so that the ctor of ClientCnxn won't get
>> too long?
>>
>> I may have missed some items. :-)
>>
>> Once again, please excuse my harsh tone. May I put the above issues in jira
>> and would you accept (backwards compatible) patches for it for 3.4.0?
>>
>> Zookeeper is a fascinating project. Cudos to the devs. I've only looked in
>> the client side code, which is what most users of zookeeper will ever see
>> if they see any zookeeper internal code at all. So it may make sense to
>> make this piece of the project as nice and clean as possible.
>>
>> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
>> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
>>
>> Best regards,
>>
>> Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Patrick Hunt <ph...@apache.org>]

Thomas, btw, if you'd like (anyone really) to do a patch extracting 
deleterecursive from zk into some helper class I think that would be a 
good idea to get sooner rather than later.

Patrick

On 08/11/2010 11:36 PM, Thomas Koch wrote:
> Patrick,
>
> I saw your patch and was afraid you wouldn't like to wait for me and change
> it. :-) I'll continue to work on my issues and also put them into jira for
> review so that my team can start to work on the new API.
> After your patch is applied, I'll adapt my patches, which should not change
> anything to the user facing API of ZK.
>
> Thomas
>
> Patrick Hunt:
>> Thomas,
>>
>> I see some patches already, which is great, however there's a
>> big/complicated refactoring that's pending here:
>>
>> https://issues.apache.org/jira/browse/ZOOKEEPER-823
>>
>> and to some extent here:
>> https://issues.apache.org/jira/browse/ZOOKEEPER-733
>>
>> and refactorings in this code prior to 733/823 going in are going to
>> cause me much pain. (esp as I'm moving code around, creating new
>> classes, etc)
>>
>> Could you hold off a bit on changes in this area until these two are
>> committed? Ben is working on the reviews now. Ben please prioritize
>> review/commit of these two.
>>
>> Patrick
>>
>> On 08/11/2010 08:23 AM, Thomas Koch wrote:
>>> Hallo Mahadev,
>>>
>>> thank you for your nice answer. Yes, we'll of cause preserve
>>> compatibility. Otherwise there is no chance to get accepted.
>>>
>>> I assume the following things must keep their interfaces:
>>> ZooKeeper (It'll call the new interface in the background),
>>> ASyncCallback, Watcher
>>> We may want to change: ClientCnxn (faktor out some things, remove dep on
>>> ZooKeeper)
>>>
>>> I think other classes should not be involved at all in our issues. My
>>> collegue Patrick was so kind to fill the jira issues.
>>>
>>> Best regards,
>>>
>>> Thomas
>>>
>>> Mahadev Konar:
>>>> Also, I am assuming you have backwards compatability in mind when you
>>>> suggest these changes right?
>>>>
>>>> The interfaces of zookeeper client should not be changing as part of
>>>> this, though the recursive delete hasn't been introduced yet (its only
>>>> available in 3.4, so we can move it out into a helper class).
>>>>
>>>> Thanks
>>>> mahadev
>>>>
>>>>
>>>> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>   wrote:
>>>>
>>>> HI Thomas,
>>>>
>>>>     I read through the list of issues you posted, most of them seem
>>>>
>>>> reasonable to fix. The one's you have mentioned below might take quite a
>>>> bit of time to fix and again a lot of testing! (just a warning :)). It
>>>> would be great if you'd want to clean this up for 3.4. Please go ahead
>>>> and file a jira. These improvements would be good to have in the
>>>> zookeeper java client.
>>>>
>>>> For deleteRecursive, I definitely agree that it should be a helper
>>>> class. I don't believe it should be in the direct zookeeper api!
>>>>
>>>> Thanks
>>>> mahadev
>>>>
>>>>
>>>> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>   wrote:
>>>>
>>>> Hi,
>>>>
>>>> I started yesterday to work on my idea of an alternative ZooKeeper
>>>> client interface.[1] Instead of methods on a ZooKeeper class, a user
>>>> should instantiate an Operation (Create, Delete, ...) and forward it to
>>>> an Executor which handles session loss errors and alikes.
>>>>
>>>> By doing that, I got shocked by the sheer number of WTF issues I found.
>>>> I'm sorry for ranting now, but it gets quicker to the poing.
>>>>
>>>> - Hostlist as string
>>>>
>>>> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule
>>>> of not doing (too much) work in a ctor. Instead the ClientCnxn should
>>>> receive an object of class "HostSet". HostSet could then be
>>>> instantiated e.g. with a comma separated string.
>>>>
>>>> - cyclic dependency ClientCnxn, ZooKeeper
>>>>
>>>> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor
>>>> builds a cyclic dependency graph between both objects. This means, you
>>>> can't have the one without the other. So why did you bother do make
>>>> them to separate classes in the first place?
>>>> ClientCnxn accesses ZooKeeper.state. State should rather be a property
>>>> of ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its
>>>> method primeConnection(). I've not yet checked, how this dependency
>>>> should be resolved better.
>>>>
>>>> - Chroot is an attribute of ClientCnxn
>>>>
>>>> I'd like to have one process that uses ZooKeeper for different things
>>>> (managing a list of work, locking some unrelated locks elsewhere). So
>>>> I've components that do this work inside the same process. These
>>>> components should get the same zookeeper-client reference chroot'ed for
>>>> their needs. So it'd be much better, if the ClientCnxn would not care
>>>> about the chroot.
>>>>
>>>> - deleteRecursive does not belong to the other methods
>>>>
>>>> DeleteRecursive has been committed to trunk already as a method to the
>>>> zookeeper class. So in the API it has the same level as the atomic
>>>> operations create, delete, getData, setData, etc. The user must get the
>>>> false impression, that deleteRecursive is also an atomic operation.
>>>> It would be better to have deleteRecursive in some helper class but not
>>>> that deep in zookeeper's core code. Maybe I'd like to have another
>>>> policy on how to react if deleteRecursive fails in the middle of its
>>>> work?
>>>>
>>>> - massive code duplication in zookeeper class
>>>>
>>>> Each operation calls validatePath, handles the chroot, calls ClientCnxn
>>>> and checks the return header for error. I'd like to address this with
>>>> the operation classes:
>>>> Each operation should receive a prechecked Path object. Calling
>>>> ClientCnxn and error checking is not (or only partly) the concern of
>>>> the operation but of an "executor" like class.
>>>>
>>>> - stat is returned by parameter
>>>>
>>>> Since one can return only one value in java it's the only choice to do
>>>> so. Still it feels more like C then like Java. However with operator
>>>> classes one could simply get the result values with getter functions
>>>> after the execution.
>>>>
>>>> - stat calls static method on org.apache.zookeeper.server.DataTree
>>>>
>>>> It's a huge jump from client code to the internal server class DataTree.
>>>> Shouldn't there rather be some class related to the protobuffer stat
>>>> class that knows how to copy a stat?
>>>>
>>>> - Session class?
>>>>
>>>> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword
>>>> and sessionTimeout in a Session class so that the ctor of ClientCnxn
>>>> won't get too long?
>>>>
>>>> I may have missed some items. :-)
>>>>
>>>> Once again, please excuse my harsh tone. May I put the above issues in
>>>> jira and would you accept (backwards compatible) patches for it for
>>>> 3.4.0?
>>>>
>>>> Zookeeper is a fascinating project. Cudos to the devs. I've only looked
>>>> in the client side code, which is what most users of zookeeper will
>>>> ever see if they see any zookeeper internal code at all. So it may make
>>>> sense to make this piece of the project as nice and clean as possible.
>>>>
>>>> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
>>>> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
>>>>
>>>> Best regards,
>>>>
>>>> Thomas Koch, http://www.koch.ro
>
> Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Patrick Hunt <ph...@apache.org>]

On 08/11/2010 11:36 PM, Thomas Koch wrote:
> I saw your patch and was afraid you wouldn't like to wait for me and change
> it. :-) I'll continue to work on my issues and also put them into jira for
> review so that my team can start to work on the new API.
> After your patch is applied, I'll adapt my patches, which should not change
> anything to the user facing API of ZK.

No problem, just didn't want you to get frustrated in case you didn't 
notice. As long as you go in with eyes wide open it's ok w/me. :-)

Patrick

>
> Patrick Hunt:
>> Thomas,
>>
>> I see some patches already, which is great, however there's a
>> big/complicated refactoring that's pending here:
>>
>> https://issues.apache.org/jira/browse/ZOOKEEPER-823
>>
>> and to some extent here:
>> https://issues.apache.org/jira/browse/ZOOKEEPER-733
>>
>> and refactorings in this code prior to 733/823 going in are going to
>> cause me much pain. (esp as I'm moving code around, creating new
>> classes, etc)
>>
>> Could you hold off a bit on changes in this area until these two are
>> committed? Ben is working on the reviews now. Ben please prioritize
>> review/commit of these two.
>>
>> Patrick
>>
>> On 08/11/2010 08:23 AM, Thomas Koch wrote:
>>> Hallo Mahadev,
>>>
>>> thank you for your nice answer. Yes, we'll of cause preserve
>>> compatibility. Otherwise there is no chance to get accepted.
>>>
>>> I assume the following things must keep their interfaces:
>>> ZooKeeper (It'll call the new interface in the background),
>>> ASyncCallback, Watcher
>>> We may want to change: ClientCnxn (faktor out some things, remove dep on
>>> ZooKeeper)
>>>
>>> I think other classes should not be involved at all in our issues. My
>>> collegue Patrick was so kind to fill the jira issues.
>>>
>>> Best regards,
>>>
>>> Thomas
>>>
>>> Mahadev Konar:
>>>> Also, I am assuming you have backwards compatability in mind when you
>>>> suggest these changes right?
>>>>
>>>> The interfaces of zookeeper client should not be changing as part of
>>>> this, though the recursive delete hasn't been introduced yet (its only
>>>> available in 3.4, so we can move it out into a helper class).
>>>>
>>>> Thanks
>>>> mahadev
>>>>
>>>>
>>>> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>   wrote:
>>>>
>>>> HI Thomas,
>>>>
>>>>     I read through the list of issues you posted, most of them seem
>>>>
>>>> reasonable to fix. The one's you have mentioned below might take quite a
>>>> bit of time to fix and again a lot of testing! (just a warning :)). It
>>>> would be great if you'd want to clean this up for 3.4. Please go ahead
>>>> and file a jira. These improvements would be good to have in the
>>>> zookeeper java client.
>>>>
>>>> For deleteRecursive, I definitely agree that it should be a helper
>>>> class. I don't believe it should be in the direct zookeeper api!
>>>>
>>>> Thanks
>>>> mahadev
>>>>
>>>>
>>>> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>   wrote:
>>>>
>>>> Hi,
>>>>
>>>> I started yesterday to work on my idea of an alternative ZooKeeper
>>>> client interface.[1] Instead of methods on a ZooKeeper class, a user
>>>> should instantiate an Operation (Create, Delete, ...) and forward it to
>>>> an Executor which handles session loss errors and alikes.
>>>>
>>>> By doing that, I got shocked by the sheer number of WTF issues I found.
>>>> I'm sorry for ranting now, but it gets quicker to the poing.
>>>>
>>>> - Hostlist as string
>>>>
>>>> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule
>>>> of not doing (too much) work in a ctor. Instead the ClientCnxn should
>>>> receive an object of class "HostSet". HostSet could then be
>>>> instantiated e.g. with a comma separated string.
>>>>
>>>> - cyclic dependency ClientCnxn, ZooKeeper
>>>>
>>>> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor
>>>> builds a cyclic dependency graph between both objects. This means, you
>>>> can't have the one without the other. So why did you bother do make
>>>> them to separate classes in the first place?
>>>> ClientCnxn accesses ZooKeeper.state. State should rather be a property
>>>> of ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its
>>>> method primeConnection(). I've not yet checked, how this dependency
>>>> should be resolved better.
>>>>
>>>> - Chroot is an attribute of ClientCnxn
>>>>
>>>> I'd like to have one process that uses ZooKeeper for different things
>>>> (managing a list of work, locking some unrelated locks elsewhere). So
>>>> I've components that do this work inside the same process. These
>>>> components should get the same zookeeper-client reference chroot'ed for
>>>> their needs. So it'd be much better, if the ClientCnxn would not care
>>>> about the chroot.
>>>>
>>>> - deleteRecursive does not belong to the other methods
>>>>
>>>> DeleteRecursive has been committed to trunk already as a method to the
>>>> zookeeper class. So in the API it has the same level as the atomic
>>>> operations create, delete, getData, setData, etc. The user must get the
>>>> false impression, that deleteRecursive is also an atomic operation.
>>>> It would be better to have deleteRecursive in some helper class but not
>>>> that deep in zookeeper's core code. Maybe I'd like to have another
>>>> policy on how to react if deleteRecursive fails in the middle of its
>>>> work?
>>>>
>>>> - massive code duplication in zookeeper class
>>>>
>>>> Each operation calls validatePath, handles the chroot, calls ClientCnxn
>>>> and checks the return header for error. I'd like to address this with
>>>> the operation classes:
>>>> Each operation should receive a prechecked Path object. Calling
>>>> ClientCnxn and error checking is not (or only partly) the concern of
>>>> the operation but of an "executor" like class.
>>>>
>>>> - stat is returned by parameter
>>>>
>>>> Since one can return only one value in java it's the only choice to do
>>>> so. Still it feels more like C then like Java. However with operator
>>>> classes one could simply get the result values with getter functions
>>>> after the execution.
>>>>
>>>> - stat calls static method on org.apache.zookeeper.server.DataTree
>>>>
>>>> It's a huge jump from client code to the internal server class DataTree.
>>>> Shouldn't there rather be some class related to the protobuffer stat
>>>> class that knows how to copy a stat?
>>>>
>>>> - Session class?
>>>>
>>>> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword
>>>> and sessionTimeout in a Session class so that the ctor of ClientCnxn
>>>> won't get too long?
>>>>
>>>> I may have missed some items. :-)
>>>>
>>>> Once again, please excuse my harsh tone. May I put the above issues in
>>>> jira and would you accept (backwards compatible) patches for it for
>>>> 3.4.0?
>>>>
>>>> Zookeeper is a fascinating project. Cudos to the devs. I've only looked
>>>> in the client side code, which is what most users of zookeeper will
>>>> ever see if they see any zookeeper internal code at all. So it may make
>>>> sense to make this piece of the project as nice and clean as possible.
>>>>
>>>> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
>>>> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
>>>>
>>>> Best regards,
>>>>
>>>> Thomas Koch, http://www.koch.ro
>
> Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Thomas Koch <th...@koch.ro>]

Patrick,

I saw your patch and was afraid you wouldn't like to wait for me and change 
it. :-) I'll continue to work on my issues and also put them into jira for 
review so that my team can start to work on the new API.
After your patch is applied, I'll adapt my patches, which should not change 
anything to the user facing API of ZK.

Thomas

Patrick Hunt:
> Thomas,
> 
> I see some patches already, which is great, however there's a
> big/complicated refactoring that's pending here:
> 
> https://issues.apache.org/jira/browse/ZOOKEEPER-823
> 
> and to some extent here:
> https://issues.apache.org/jira/browse/ZOOKEEPER-733
> 
> and refactorings in this code prior to 733/823 going in are going to
> cause me much pain. (esp as I'm moving code around, creating new
> classes, etc)
> 
> Could you hold off a bit on changes in this area until these two are
> committed? Ben is working on the reviews now. Ben please prioritize
> review/commit of these two.
> 
> Patrick
> 
> On 08/11/2010 08:23 AM, Thomas Koch wrote:
> > Hallo Mahadev,
> > 
> > thank you for your nice answer. Yes, we'll of cause preserve
> > compatibility. Otherwise there is no chance to get accepted.
> > 
> > I assume the following things must keep their interfaces:
> > ZooKeeper (It'll call the new interface in the background),
> > ASyncCallback, Watcher
> > We may want to change: ClientCnxn (faktor out some things, remove dep on
> > ZooKeeper)
> > 
> > I think other classes should not be involved at all in our issues. My
> > collegue Patrick was so kind to fill the jira issues.
> > 
> > Best regards,
> > 
> > Thomas
> > 
> > Mahadev Konar:
> >> Also, I am assuming you have backwards compatability in mind when you
> >> suggest these changes right?
> >> 
> >> The interfaces of zookeeper client should not be changing as part of
> >> this, though the recursive delete hasn't been introduced yet (its only
> >> available in 3.4, so we can move it out into a helper class).
> >> 
> >> Thanks
> >> mahadev
> >> 
> >> 
> >> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>  wrote:
> >> 
> >> HI Thomas,
> >> 
> >>    I read through the list of issues you posted, most of them seem
> >> 
> >> reasonable to fix. The one's you have mentioned below might take quite a
> >> bit of time to fix and again a lot of testing! (just a warning :)). It
> >> would be great if you'd want to clean this up for 3.4. Please go ahead
> >> and file a jira. These improvements would be good to have in the
> >> zookeeper java client.
> >> 
> >> For deleteRecursive, I definitely agree that it should be a helper
> >> class. I don't believe it should be in the direct zookeeper api!
> >> 
> >> Thanks
> >> mahadev
> >> 
> >> 
> >> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>  wrote:
> >> 
> >> Hi,
> >> 
> >> I started yesterday to work on my idea of an alternative ZooKeeper
> >> client interface.[1] Instead of methods on a ZooKeeper class, a user
> >> should instantiate an Operation (Create, Delete, ...) and forward it to
> >> an Executor which handles session loss errors and alikes.
> >> 
> >> By doing that, I got shocked by the sheer number of WTF issues I found.
> >> I'm sorry for ranting now, but it gets quicker to the poing.
> >> 
> >> - Hostlist as string
> >> 
> >> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule
> >> of not doing (too much) work in a ctor. Instead the ClientCnxn should
> >> receive an object of class "HostSet". HostSet could then be
> >> instantiated e.g. with a comma separated string.
> >> 
> >> - cyclic dependency ClientCnxn, ZooKeeper
> >> 
> >> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor
> >> builds a cyclic dependency graph between both objects. This means, you
> >> can't have the one without the other. So why did you bother do make
> >> them to separate classes in the first place?
> >> ClientCnxn accesses ZooKeeper.state. State should rather be a property
> >> of ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its
> >> method primeConnection(). I've not yet checked, how this dependency
> >> should be resolved better.
> >> 
> >> - Chroot is an attribute of ClientCnxn
> >> 
> >> I'd like to have one process that uses ZooKeeper for different things
> >> (managing a list of work, locking some unrelated locks elsewhere). So
> >> I've components that do this work inside the same process. These
> >> components should get the same zookeeper-client reference chroot'ed for
> >> their needs. So it'd be much better, if the ClientCnxn would not care
> >> about the chroot.
> >> 
> >> - deleteRecursive does not belong to the other methods
> >> 
> >> DeleteRecursive has been committed to trunk already as a method to the
> >> zookeeper class. So in the API it has the same level as the atomic
> >> operations create, delete, getData, setData, etc. The user must get the
> >> false impression, that deleteRecursive is also an atomic operation.
> >> It would be better to have deleteRecursive in some helper class but not
> >> that deep in zookeeper's core code. Maybe I'd like to have another
> >> policy on how to react if deleteRecursive fails in the middle of its
> >> work?
> >> 
> >> - massive code duplication in zookeeper class
> >> 
> >> Each operation calls validatePath, handles the chroot, calls ClientCnxn
> >> and checks the return header for error. I'd like to address this with
> >> the operation classes:
> >> Each operation should receive a prechecked Path object. Calling
> >> ClientCnxn and error checking is not (or only partly) the concern of
> >> the operation but of an "executor" like class.
> >> 
> >> - stat is returned by parameter
> >> 
> >> Since one can return only one value in java it's the only choice to do
> >> so. Still it feels more like C then like Java. However with operator
> >> classes one could simply get the result values with getter functions
> >> after the execution.
> >> 
> >> - stat calls static method on org.apache.zookeeper.server.DataTree
> >> 
> >> It's a huge jump from client code to the internal server class DataTree.
> >> Shouldn't there rather be some class related to the protobuffer stat
> >> class that knows how to copy a stat?
> >> 
> >> - Session class?
> >> 
> >> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword
> >> and sessionTimeout in a Session class so that the ctor of ClientCnxn
> >> won't get too long?
> >> 
> >> I may have missed some items. :-)
> >> 
> >> Once again, please excuse my harsh tone. May I put the above issues in
> >> jira and would you accept (backwards compatible) patches for it for
> >> 3.4.0?
> >> 
> >> Zookeeper is a fascinating project. Cudos to the devs. I've only looked
> >> in the client side code, which is what most users of zookeeper will
> >> ever see if they see any zookeeper internal code at all. So it may make
> >> sense to make this piece of the project as nice and clean as possible.
> >> 
> >> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
> >> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
> >> 
> >> Best regards,
> >> 
> >> Thomas Koch, http://www.koch.ro

Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Patrick Hunt <ph...@apache.org>]

Thomas,

I see some patches already, which is great, however there's a 
big/complicated refactoring that's pending here:

https://issues.apache.org/jira/browse/ZOOKEEPER-823

and to some extent here:
https://issues.apache.org/jira/browse/ZOOKEEPER-733

and refactorings in this code prior to 733/823 going in are going to 
cause me much pain. (esp as I'm moving code around, creating new 
classes, etc)

Could you hold off a bit on changes in this area until these two are 
committed? Ben is working on the reviews now. Ben please prioritize 
review/commit of these two.

Patrick

On 08/11/2010 08:23 AM, Thomas Koch wrote:
> Hallo Mahadev,
>
> thank you for your nice answer. Yes, we'll of cause preserve compatibility.
> Otherwise there is no chance to get accepted.
>
> I assume the following things must keep their interfaces:
> ZooKeeper (It'll call the new interface in the background), ASyncCallback,
> Watcher
> We may want to change: ClientCnxn (faktor out some things, remove dep on
> ZooKeeper)
>
> I think other classes should not be involved at all in our issues. My collegue
> Patrick was so kind to fill the jira issues.
>
> Best regards,
>
> Thomas
>
>
> Mahadev Konar:
>> Also, I am assuming you have backwards compatability in mind when you
>> suggest these changes right?
>>
>> The interfaces of zookeeper client should not be changing as part of this,
>> though the recursive delete hasn't been introduced yet (its only available
>> in 3.4, so we can move it out into a helper class).
>>
>> Thanks
>> mahadev
>>
>>
>> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>  wrote:
>>
>> HI Thomas,
>>    I read through the list of issues you posted, most of them seem
>> reasonable to fix. The one's you have mentioned below might take quite a
>> bit of time to fix and again a lot of testing! (just a warning :)). It
>> would be great if you'd want to clean this up for 3.4. Please go ahead and
>> file a jira. These improvements would be good to have in the zookeeper
>> java client.
>>
>> For deleteRecursive, I definitely agree that it should be a helper class. I
>> don't believe it should be in the direct zookeeper api!
>>
>> Thanks
>> mahadev
>>
>>
>> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>  wrote:
>>
>> Hi,
>>
>> I started yesterday to work on my idea of an alternative ZooKeeper client
>> interface.[1] Instead of methods on a ZooKeeper class, a user should
>> instantiate an Operation (Create, Delete, ...) and forward it to an
>> Executor which handles session loss errors and alikes.
>>
>> By doing that, I got shocked by the sheer number of WTF issues I found. I'm
>> sorry for ranting now, but it gets quicker to the poing.
>>
>> - Hostlist as string
>>
>> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
>> not doing (too much) work in a ctor. Instead the ClientCnxn should receive
>> an object of class "HostSet". HostSet could then be instantiated e.g. with
>> a comma separated string.
>>
>> - cyclic dependency ClientCnxn, ZooKeeper
>>
>> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds
>> a cyclic dependency graph between both objects. This means, you can't have
>> the one without the other. So why did you bother do make them to separate
>> classes in the first place?
>> ClientCnxn accesses ZooKeeper.state. State should rather be a property of
>> ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
>> primeConnection(). I've not yet checked, how this dependency should be
>> resolved better.
>>
>> - Chroot is an attribute of ClientCnxn
>>
>> I'd like to have one process that uses ZooKeeper for different things
>> (managing a list of work, locking some unrelated locks elsewhere). So I've
>> components that do this work inside the same process. These components
>> should get the same zookeeper-client reference chroot'ed for their needs.
>> So it'd be much better, if the ClientCnxn would not care about the chroot.
>>
>> - deleteRecursive does not belong to the other methods
>>
>> DeleteRecursive has been committed to trunk already as a method to the
>> zookeeper class. So in the API it has the same level as the atomic
>> operations create, delete, getData, setData, etc. The user must get the
>> false impression, that deleteRecursive is also an atomic operation.
>> It would be better to have deleteRecursive in some helper class but not
>> that deep in zookeeper's core code. Maybe I'd like to have another policy
>> on how to react if deleteRecursive fails in the middle of its work?
>>
>> - massive code duplication in zookeeper class
>>
>> Each operation calls validatePath, handles the chroot, calls ClientCnxn and
>> checks the return header for error. I'd like to address this with the
>> operation classes:
>> Each operation should receive a prechecked Path object. Calling ClientCnxn
>> and error checking is not (or only partly) the concern of the operation
>> but of an "executor" like class.
>>
>> - stat is returned by parameter
>>
>> Since one can return only one value in java it's the only choice to do so.
>> Still it feels more like C then like Java. However with operator classes
>> one could simply get the result values with getter functions after the
>> execution.
>>
>> - stat calls static method on org.apache.zookeeper.server.DataTree
>>
>> It's a huge jump from client code to the internal server class DataTree.
>> Shouldn't there rather be some class related to the protobuffer stat class
>> that knows how to copy a stat?
>>
>> - Session class?
>>
>> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
>> sessionTimeout in a Session class so that the ctor of ClientCnxn won't get
>> too long?
>>
>> I may have missed some items. :-)
>>
>> Once again, please excuse my harsh tone. May I put the above issues in jira
>> and would you accept (backwards compatible) patches for it for 3.4.0?
>>
>> Zookeeper is a fascinating project. Cudos to the devs. I've only looked in
>> the client side code, which is what most users of zookeeper will ever see
>> if they see any zookeeper internal code at all. So it may make sense to
>> make this piece of the project as nice and clean as possible.
>>
>> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
>> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
>>
>> Best regards,
>>
>> Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Thomas Koch <th...@koch.ro>]

Hallo Mahadev,

thank you for your nice answer. Yes, we'll of cause preserve compatibility. 
Otherwise there is no chance to get accepted.

I assume the following things must keep their interfaces:
ZooKeeper (It'll call the new interface in the background), ASyncCallback, 
Watcher
We may want to change: ClientCnxn (faktor out some things, remove dep on 
ZooKeeper)

I think other classes should not be involved at all in our issues. My collegue 
Patrick was so kind to fill the jira issues.

Best regards,

Thomas


Mahadev Konar:
> Also, I am assuming you have backwards compatability in mind when you
> suggest these changes right?
> 
> The interfaces of zookeeper client should not be changing as part of this,
> though the recursive delete hasn't been introduced yet (its only available
> in 3.4, so we can move it out into a helper class).
> 
> Thanks
> mahadev
> 
> 
> On 8/11/10 7:40 AM, "Mahadev Konar" <ma...@yahoo-inc.com> wrote:
> 
> HI Thomas,
>   I read through the list of issues you posted, most of them seem
> reasonable to fix. The one's you have mentioned below might take quite a
> bit of time to fix and again a lot of testing! (just a warning :)). It
> would be great if you'd want to clean this up for 3.4. Please go ahead and
> file a jira. These improvements would be good to have in the zookeeper
> java client.
> 
> For deleteRecursive, I definitely agree that it should be a helper class. I
> don't believe it should be in the direct zookeeper api!
> 
> Thanks
> mahadev
> 
> 
> On 8/11/10 2:45 AM, "Thomas Koch" <th...@koch.ro> wrote:
> 
> Hi,
> 
> I started yesterday to work on my idea of an alternative ZooKeeper client
> interface.[1] Instead of methods on a ZooKeeper class, a user should
> instantiate an Operation (Create, Delete, ...) and forward it to an
> Executor which handles session loss errors and alikes.
> 
> By doing that, I got shocked by the sheer number of WTF issues I found. I'm
> sorry for ranting now, but it gets quicker to the poing.
> 
> - Hostlist as string
> 
> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
> not doing (too much) work in a ctor. Instead the ClientCnxn should receive
> an object of class "HostSet". HostSet could then be instantiated e.g. with
> a comma separated string.
> 
> - cyclic dependency ClientCnxn, ZooKeeper
> 
> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds
> a cyclic dependency graph between both objects. This means, you can't have
> the one without the other. So why did you bother do make them to separate
> classes in the first place?
> ClientCnxn accesses ZooKeeper.state. State should rather be a property of
> ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
> primeConnection(). I've not yet checked, how this dependency should be
> resolved better.
> 
> - Chroot is an attribute of ClientCnxn
> 
> I'd like to have one process that uses ZooKeeper for different things
> (managing a list of work, locking some unrelated locks elsewhere). So I've
> components that do this work inside the same process. These components
> should get the same zookeeper-client reference chroot'ed for their needs.
> So it'd be much better, if the ClientCnxn would not care about the chroot.
> 
> - deleteRecursive does not belong to the other methods
> 
> DeleteRecursive has been committed to trunk already as a method to the
> zookeeper class. So in the API it has the same level as the atomic
> operations create, delete, getData, setData, etc. The user must get the
> false impression, that deleteRecursive is also an atomic operation.
> It would be better to have deleteRecursive in some helper class but not
> that deep in zookeeper's core code. Maybe I'd like to have another policy
> on how to react if deleteRecursive fails in the middle of its work?
> 
> - massive code duplication in zookeeper class
> 
> Each operation calls validatePath, handles the chroot, calls ClientCnxn and
> checks the return header for error. I'd like to address this with the
> operation classes:
> Each operation should receive a prechecked Path object. Calling ClientCnxn
> and error checking is not (or only partly) the concern of the operation
> but of an "executor" like class.
> 
> - stat is returned by parameter
> 
> Since one can return only one value in java it's the only choice to do so.
> Still it feels more like C then like Java. However with operator classes
> one could simply get the result values with getter functions after the
> execution.
> 
> - stat calls static method on org.apache.zookeeper.server.DataTree
> 
> It's a huge jump from client code to the internal server class DataTree.
> Shouldn't there rather be some class related to the protobuffer stat class
> that knows how to copy a stat?
> 
> - Session class?
> 
> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
> sessionTimeout in a Session class so that the ctor of ClientCnxn won't get
> too long?
> 
> I may have missed some items. :-)
> 
> Once again, please excuse my harsh tone. May I put the above issues in jira
> and would you accept (backwards compatible) patches for it for 3.4.0?
> 
> Zookeeper is a fascinating project. Cudos to the devs. I've only looked in
> the client side code, which is what most users of zookeeper will ever see
> if they see any zookeeper internal code at all. So it may make sense to
> make this piece of the project as nice and clean as possible.
> 
> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
> 
> Best regards,
> 
> Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Maarten Koopmans <ma...@vrijheid.net>]

Off note: I have a Scala wrapper on the Java client (sync only) that has 
these functions:

- treeAsList(path: String)
- processTree(path: String,f: (String -> Unit))

This implements recursive delete as a processTree(path,delete_), but 
also a recursive copy and move if need be.

Just my two cents (when I'm back from holiday I will look at the 
contribute wiki and send add-ons)

Best, Maarten

On 08/11/2010 04:50 PM, Mahadev Konar wrote:
> Also, I am assuming you have backwards compatability in mind when you suggest these changes right?
>
> The interfaces of zookeeper client should not be changing as part of this, though the recursive delete hasn't been introduced yet (its only available in 3.4, so we can move it out into a helper class).
>
> Thanks
> mahadev
>
>
> On 8/11/10 7:40 AM, "Mahadev Konar"<ma...@yahoo-inc.com>  wrote:
>
> HI Thomas,
>    I read through the list of issues you posted, most of them seem reasonable to fix. The one's you have mentioned below might take quite a bit of time to fix and again a lot of testing! (just a warning :)). It would be great if you'd want to clean this up for 3.4. Please go ahead and file a jira. These improvements would be good to have in the zookeeper java client.
>
> For deleteRecursive, I definitely agree that it should be a helper class. I don't believe it should be in the direct zookeeper api!
>
> Thanks
> mahadev
>
>
> On 8/11/10 2:45 AM, "Thomas Koch"<th...@koch.ro>  wrote:
>
> Hi,
>
> I started yesterday to work on my idea of an alternative ZooKeeper client
> interface.[1] Instead of methods on a ZooKeeper class, a user should
> instantiate an Operation (Create, Delete, ...) and forward it to an Executor
> which handles session loss errors and alikes.
>
> By doing that, I got shocked by the sheer number of WTF issues I found. I'm
> sorry for ranting now, but it gets quicker to the poing.
>
> - Hostlist as string
>
> The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
> not doing (too much) work in a ctor. Instead the ClientCnxn should receive an
> object of class "HostSet". HostSet could then be instantiated e.g. with a
> comma separated string.
>
> - cyclic dependency ClientCnxn, ZooKeeper
>
> ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds a
> cyclic dependency graph between both objects. This means, you can't have the
> one without the other. So why did you bother do make them to separate classes
> in the first place?
> ClientCnxn accesses ZooKeeper.state. State should rather be a property of
> ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
> primeConnection(). I've not yet checked, how this dependency should be
> resolved better.
>
> - Chroot is an attribute of ClientCnxn
>
> I'd like to have one process that uses ZooKeeper for different things
> (managing a list of work, locking some unrelated locks elsewhere). So I've
> components that do this work inside the same process. These components should
> get the same zookeeper-client reference chroot'ed for their needs.
> So it'd be much better, if the ClientCnxn would not care about the chroot.
>
> - deleteRecursive does not belong to the other methods
>
> DeleteRecursive has been committed to trunk already as a method to the
> zookeeper class. So in the API it has the same level as the atomic operations
> create, delete, getData, setData, etc. The user must get the false impression,
> that deleteRecursive is also an atomic operation.
> It would be better to have deleteRecursive in some helper class but not that
> deep in zookeeper's core code. Maybe I'd like to have another policy on how to
> react if deleteRecursive fails in the middle of its work?
>
> - massive code duplication in zookeeper class
>
> Each operation calls validatePath, handles the chroot, calls ClientCnxn and
> checks the return header for error. I'd like to address this with the
> operation classes:
> Each operation should receive a prechecked Path object. Calling ClientCnxn and
> error checking is not (or only partly) the concern of the operation but of an
> "executor" like class.
>
> - stat is returned by parameter
>
> Since one can return only one value in java it's the only choice to do so.
> Still it feels more like C then like Java. However with operator classes one
> could simply get the result values with getter functions after the execution.
>
> - stat calls static method on org.apache.zookeeper.server.DataTree
>
> It's a huge jump from client code to the internal server class DataTree.
> Shouldn't there rather be some class related to the protobuffer stat class
> that knows how to copy a stat?
>
> - Session class?
>
> Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
> sessionTimeout in a Session class so that the ctor of ClientCnxn won't get too
> long?
>
> I may have missed some items. :-)
>
> Once again, please excuse my harsh tone. May I put the above issues in jira
> and would you accept (backwards compatible) patches for it for 3.4.0?
>
> Zookeeper is a fascinating project. Cudos to the devs. I've only looked in the
> client side code, which is what most users of zookeeper will ever see if they
> see any zookeeper internal code at all. So it may make sense to make this
> piece of the project as nice and clean as possible.
>
> [1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
> dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E
>
> Best regards,
>
> Thomas Koch, http://www.koch.ro
>
>
>

Re: High WTF count in ZooKeeper client code

[Mahadev Konar <ma...@yahoo-inc.com>]

Also, I am assuming you have backwards compatability in mind when you suggest these changes right?

The interfaces of zookeeper client should not be changing as part of this, though the recursive delete hasn't been introduced yet (its only available in 3.4, so we can move it out into a helper class).

Thanks
mahadev


On 8/11/10 7:40 AM, "Mahadev Konar" <ma...@yahoo-inc.com> wrote:

HI Thomas,
  I read through the list of issues you posted, most of them seem reasonable to fix. The one's you have mentioned below might take quite a bit of time to fix and again a lot of testing! (just a warning :)). It would be great if you'd want to clean this up for 3.4. Please go ahead and file a jira. These improvements would be good to have in the zookeeper java client.

For deleteRecursive, I definitely agree that it should be a helper class. I don't believe it should be in the direct zookeeper api!

Thanks
mahadev


On 8/11/10 2:45 AM, "Thomas Koch" <th...@koch.ro> wrote:

Hi,

I started yesterday to work on my idea of an alternative ZooKeeper client
interface.[1] Instead of methods on a ZooKeeper class, a user should
instantiate an Operation (Create, Delete, ...) and forward it to an Executor
which handles session loss errors and alikes.

By doing that, I got shocked by the sheer number of WTF issues I found. I'm
sorry for ranting now, but it gets quicker to the poing.

- Hostlist as string

The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
not doing (too much) work in a ctor. Instead the ClientCnxn should receive an
object of class "HostSet". HostSet could then be instantiated e.g. with a
comma separated string.

- cyclic dependency ClientCnxn, ZooKeeper

ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds a
cyclic dependency graph between both objects. This means, you can't have the
one without the other. So why did you bother do make them to separate classes
in the first place?
ClientCnxn accesses ZooKeeper.state. State should rather be a property of
ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
primeConnection(). I've not yet checked, how this dependency should be
resolved better.

- Chroot is an attribute of ClientCnxn

I'd like to have one process that uses ZooKeeper for different things
(managing a list of work, locking some unrelated locks elsewhere). So I've
components that do this work inside the same process. These components should
get the same zookeeper-client reference chroot'ed for their needs.
So it'd be much better, if the ClientCnxn would not care about the chroot.

- deleteRecursive does not belong to the other methods

DeleteRecursive has been committed to trunk already as a method to the
zookeeper class. So in the API it has the same level as the atomic operations
create, delete, getData, setData, etc. The user must get the false impression,
that deleteRecursive is also an atomic operation.
It would be better to have deleteRecursive in some helper class but not that
deep in zookeeper's core code. Maybe I'd like to have another policy on how to
react if deleteRecursive fails in the middle of its work?

- massive code duplication in zookeeper class

Each operation calls validatePath, handles the chroot, calls ClientCnxn and
checks the return header for error. I'd like to address this with the
operation classes:
Each operation should receive a prechecked Path object. Calling ClientCnxn and
error checking is not (or only partly) the concern of the operation but of an
"executor" like class.

- stat is returned by parameter

Since one can return only one value in java it's the only choice to do so.
Still it feels more like C then like Java. However with operator classes one
could simply get the result values with getter functions after the execution.

- stat calls static method on org.apache.zookeeper.server.DataTree

It's a huge jump from client code to the internal server class DataTree.
Shouldn't there rather be some class related to the protobuffer stat class
that knows how to copy a stat?

- Session class?

Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
sessionTimeout in a Session class so that the ctor of ClientCnxn won't get too
long?

I may have missed some items. :-)

Once again, please excuse my harsh tone. May I put the above issues in jira
and would you accept (backwards compatible) patches for it for 3.4.0?

Zookeeper is a fascinating project. Cudos to the devs. I've only looked in the
client side code, which is what most users of zookeeper will ever see if they
see any zookeeper internal code at all. So it may make sense to make this
piece of the project as nice and clean as possible.

[1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E

Best regards,

Thomas Koch, http://www.koch.ro

Re: High WTF count in ZooKeeper client code

[Mahadev Konar <ma...@yahoo-inc.com>]

HI Thomas,
  I read through the list of issues you posted, most of them seem reasonable to fix. The one's you have mentioned below might take quite a bit of time to fix and again a lot of testing! (just a warning :)). It would be great if you'd want to clean this up for 3.4. Please go ahead and file a jira. These improvements would be good to have in the zookeeper java client.

For deleteRecursive, I definitely agree that it should be a helper class. I don't believe it should be in the direct zookeeper api!

Thanks
mahadev


On 8/11/10 2:45 AM, "Thomas Koch" <th...@koch.ro> wrote:

Hi,

I started yesterday to work on my idea of an alternative ZooKeeper client
interface.[1] Instead of methods on a ZooKeeper class, a user should
instantiate an Operation (Create, Delete, ...) and forward it to an Executor
which handles session loss errors and alikes.

By doing that, I got shocked by the sheer number of WTF issues I found. I'm
sorry for ranting now, but it gets quicker to the poing.

- Hostlist as string

The hostlist is parsed in the ctor of ClientCnxn. This violates the rule of
not doing (too much) work in a ctor. Instead the ClientCnxn should receive an
object of class "HostSet". HostSet could then be instantiated e.g. with a
comma separated string.

- cyclic dependency ClientCnxn, ZooKeeper

ZooKeeper instantiates ClientCnxn in its ctor with this and therefor builds a
cyclic dependency graph between both objects. This means, you can't have the
one without the other. So why did you bother do make them to separate classes
in the first place?
ClientCnxn accesses ZooKeeper.state. State should rather be a property of
ClientCnxn. And ClientCnxn accesses zooKeeper.get???Watches() in its method
primeConnection(). I've not yet checked, how this dependency should be
resolved better.

- Chroot is an attribute of ClientCnxn

I'd like to have one process that uses ZooKeeper for different things
(managing a list of work, locking some unrelated locks elsewhere). So I've
components that do this work inside the same process. These components should
get the same zookeeper-client reference chroot'ed for their needs.
So it'd be much better, if the ClientCnxn would not care about the chroot.

- deleteRecursive does not belong to the other methods

DeleteRecursive has been committed to trunk already as a method to the
zookeeper class. So in the API it has the same level as the atomic operations
create, delete, getData, setData, etc. The user must get the false impression,
that deleteRecursive is also an atomic operation.
It would be better to have deleteRecursive in some helper class but not that
deep in zookeeper's core code. Maybe I'd like to have another policy on how to
react if deleteRecursive fails in the middle of its work?

- massive code duplication in zookeeper class

Each operation calls validatePath, handles the chroot, calls ClientCnxn and
checks the return header for error. I'd like to address this with the
operation classes:
Each operation should receive a prechecked Path object. Calling ClientCnxn and
error checking is not (or only partly) the concern of the operation but of an
"executor" like class.

- stat is returned by parameter

Since one can return only one value in java it's the only choice to do so.
Still it feels more like C then like Java. However with operator classes one
could simply get the result values with getter functions after the execution.

- stat calls static method on org.apache.zookeeper.server.DataTree

It's a huge jump from client code to the internal server class DataTree.
Shouldn't there rather be some class related to the protobuffer stat class
that knows how to copy a stat?

- Session class?

Maybe it'd make sense to combine hostlist, sessionId, sessionPassword and
sessionTimeout in a Session class so that the ctor of ClientCnxn won't get too
long?

I may have missed some items. :-)

Once again, please excuse my harsh tone. May I put the above issues in jira
and would you accept (backwards compatible) patches for it for 3.4.0?

Zookeeper is a fascinating project. Cudos to the devs. I've only looked in the
client side code, which is what most users of zookeeper will ever see if they
see any zookeeper internal code at all. So it may make sense to make this
piece of the project as nice and clean as possible.

[1] http://mail-archives.apache.org/mod_mbox/hadoop-zookeeper-
dev/201005.mbox/%3C201005261509.54236.thomas@koch.ro%3E

Best regards,

Thomas Koch, http://www.koch.ro