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Accumulo >> mail # dev >> Hadoop 2 compatibility issues


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Re: Hadoop 2 compatibility issues
Yes, they should add a dependency on Hadoop, if they use it. The
problem isn't just if they use Hadoop classes, though. It is that the
dependency is required for any code path where Accumulo requires
Hadoop... and this is unknown to the user, because the dependency tree
looks like Accumulo has no dependency on Hadoop at all. They certainly
won't know which Hadoop jars to add, without deep inspection of
Accumulo's profiles.

--
Christopher L Tubbs II
http://gravatar.com/ctubbsii
On Tue, May 14, 2013 at 4:52 PM, Sean Busbey <[EMAIL PROTECTED]> wrote:
> If a user is referencing any of the Hadoop classes, aren't they supposed to
> add a dependency on the appropriate Hadoop artifact anyways?
>
> FWIW, option 4 is what Avro does. Their discussion:
>
> https://issues.apache.org/jira/browse/AVRO-1170
>
>
>
>
> On Tue, May 14, 2013 at 4:40 PM, Christopher <[EMAIL PROTECTED]> wrote:
>
>> So, I've run into a problem with ACCUMULO-1402 that requires a larger
>> discussion about how Accumulo 1.5.0 should support Hadoop2.
>>
>> The problem is basically that profiles should not contain
>> dependencies, because profiles don't get activated transitively. A
>> slide deck by the Maven developers point this out as a bad practice...
>> yet it's a practice we rely on for our current implementation of
>> Hadoop2 support
>> (http://www.slideshare.net/aheritier/geneva-jug-30th-march-2010-maven
>> slide 80).
>>
>> What this means is that even if we go through the work of publishing
>> binary artifacts compiled against Hadoop2, neither our Hadoop1
>> binaries or our Hadoop2 binaries will be able to transitively resolve
>> any dependencies defined in profiles. This has significant
>> implications to user code that depends on Accumulo Maven artifacts.
>> Every user will essentially have to explicitly add Hadoop dependencies
>> for every Accumulo artifact that has dependencies on Hadoop, either
>> because we directly or transitively depend on Hadoop (they'll have to
>> peek into the profiles in our POMs and copy/paste the profile into
>> their project). This becomes more complicated when we consider how
>> users will try to use things like Instamo.
>>
>> There are workarounds, but none of them are really pleasant.
>>
>> 1. The best way to support both major Hadoop APIs is to have separate
>> modules with separate dependencies directly in the POM. This is a fair
>> amount of work, and in my opinion, would be too disruptive for 1.5.0.
>> This solution also gets us separate binaries for separate supported
>> versions, which is useful.
>>
>> 2. A second option, and the preferred one I think for 1.5.0, is to put
>> a Hadoop2 patch in the branch's contrib directory
>> (branches/1.5/contrib) that patches the POM files to support building
>> against Hadoop2. (Acknowledgement to Keith for suggesting this
>> solution.)
>>
>> 3. A third option is to fork Accumulo, and maintain two separate
>> builds (a more traditional technique). This adds merging nightmare for
>> features/patches, but gets around some reflection hacks that we may
>> have been motivated to do in the past. I'm not a fan of this option,
>> particularly because I don't want to replicate the fork nightmare that
>> has been the history of early Hadoop itself.
>>
>> 4. The last option is to do nothing and to continue to build with the
>> separate profiles as we are, and make users discover and specify
>> transitive dependencies entirely on their own. I think this is the
>> worst option, as it essentially amounts to "ignore the problem".
>>
>> At the very least, it does not seem reasonable to complete
>> ACCUMULO-1402 for 1.5.0, given the complexity of this issue.
>>
>> Thoughts? Discussion? Vote on option?
>>
>> --
>> Christopher L Tubbs II
>> http://gravatar.com/ctubbsii
>>
>
>
>
> --
> Sean Busbey
> Solutions Architect
> Cloudera, Inc.
> Phone: MAN-VS-BEARD