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From Benson Margulies <>
Subject Re: Hadoop 2 compatibility issues
Date Tue, 14 May 2013 21:51:20 GMT
I am a maven developer, and I'm offering this advice based on my
understanding of reason why that generic advice is offered.

If you have different profiles that _build different results_ but all
deliver the same GAV, you have chaos.

If you have different profiles that test against different versions of
dependencies, but all deliver the same byte code at the end of the
day, you don't have chaos.

On Tue, May 14, 2013 at 5:48 PM, Christopher <> wrote:
> I think it's interesting that Option 4 seems to be most preferred...
> because it's the *only* option that is explicitly advised against by
> the Maven developers (from the information I've read). I can see its
> appeal, but I really don't think that we should introduce an explicit
> problem for users (that applies to users using even the Hadoop version
> we directly build against... not just those using Hadoop 2... I don't
> know if that point was clear), to only partially support a version of
> Hadoop that is still alpha and has never had a stable release.
> BTW, Option 4 was how I had have achieved a solution for
> ACCUMULO-1402, but am reluctant to apply that patch, with this issue
> outstanding, as it may exacerbate the problem.
> Another implication for Option 4 (the current "solution") is for
> 1.6.0, with the planned accumulo-maven-plugin... because it means that
> the accumulo-maven-plugin will need to be configured like this:
> <plugin>
>   <groupId>org.apache.accumulo</groupId>
>   <artifactId>accumulo-maven-plugin</artifactId>
>   <dependencies>
>    ... all the required hadoop 1 dependencies to make the plugin work,
> even though this version only works against hadoop 1 anyway...
>   </dependencies>
>   ...
> </plugin>
> --
> Christopher L Tubbs II
> On Tue, May 14, 2013 at 5:42 PM, Christopher <> wrote:
>> I think Option 2 is the best solution for "waiting until we have the
>> time to solve the problem correctly", as it ensures that transitive
>> dependencies work for the stable version of Hadoop, and using Hadoop2
>> is a very simple documentation issue for how to apply the patch and
>> rebuild. Option 4 doesn't wait... it explicitly introduces a problem
>> for users.
>> Option 1 is how I'm tentatively thinking about fixing it properly in 1.6.0.
>> --
>> Christopher L Tubbs II
>> On Tue, May 14, 2013 at 4:56 PM, John Vines <> wrote:
>>> I'm an advocate of option 4. You say that it's ignoring the problem,
>>> whereas I think it's waiting until we have the time to solve the problem
>>> correctly. Your reasoning for this is for standardizing for maven
>>> conventions, but the other options, while more 'correct' from a maven
>>> standpoint or a larger headache for our user base and ourselves. In either
>>> case, we're going to be breaking some sort of convention, and while it's
>>> not good, we should be doing the one that's less bad for US. The important
>>> thing here, now, is that the poms work and we should go with the method
>>> that leaves the work minimal for our end users to utilize them.
>>> I do agree that 1. is the correct option in the long run. More
>>> specifically, I think it boils down to having a single module compatibility
>>> layer, which is how hbase deals with this issue. But like you said, we
>>> don't have the time to engineer a proper solution. So let sleeping dogs lie
>>> and we can revamp the whole system for 1.5.1 or 1.6.0 when we have the
>>> cycles to do it right.
>>> On Tue, May 14, 2013 at 4:40 PM, Christopher <> 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
>>>> (
>>>> 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

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