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>]

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
> 
>