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From Hitesh Shah <hit...@apache.org>
Subject Re: [DISCUSS] Publishing and releasing jars for different hadoop version dependencies
Date Fri, 06 Mar 2015 19:03:03 GMT
Thanks for the feedback, Kostas, 

One clarification though - are you saying Tez should publish jars to maven central built against
different versions of Hadoop? If yes, is this mainly due to the hadoop dependencies that Tez
pulls in or due to any incompatibilities that you have noticed? 

— Hitesh

On Mar 6, 2015, at 9:03 AM, Kostas Tzoumas <ktzoumas@apache.org> wrote:

> Publishing jars for different Hadoop dependencies, and in particular for
> Hadoop 2.2 would also be beneficial for Flink on Tez as we offer maven
> archetypes for users to create Flink applications.  Currently, we need to
> ask users that want to run Flink apps with Tez as backend to compile the
> Flink code themselves due to a Hadoop version mismatch.
> On Thu, Mar 5, 2015 at 1:46 AM, Hitesh Shah <hitesh@apache.org> wrote:
>> From an ASF perspective, verifiable releases are only source releases. The
>> binaries are just convenience artifacts that can also made available with a
>> given release. Hence in terms of supporting multiple hadoop versions, we do
>> want to allow various users/distros to compile Tez against their particular
>> version of hadoop.
>> From a run-time point of view , if Tez compiled against hadoop-2.6 is run
>> on a 2.4 cluster, it should work normally as long as acls are disabled (
>> via tez config tez.am.acls.enabled ). That said, there are probably some
>> improvements that could be done to handle the case where acls are enabled
>> on a 2.4 cluster in a more cleaner manner.
>> thanks
>> — Hitesh
>> On Mar 4, 2015, at 9:21 AM, Chris K Wensel <chris@wensel.net> wrote:
>>> compile what against hadoop 2.4? Tez? Hopefully no one except Tez devs
>> ever compile Tez (once the apache committers offer up pre-built binaries, I
>> only ever do for this reason).
>>> if compiling application code against Tez and Hadoop 2.4, the jar won't
>> come into play unless running tests (so i believe).
>>> I would then enhance option two to gracefully fail if -acls (the
>> Manager) is not applicable (on hadoop 2.4) but mistakenly included in the
>> 2.4 classpath (testing app code against hadoop 2.4)
>>> of course then this is really option 1 now with two jars.
>>> ckw
>>>> On Mar 2, 2015, at 3:05 PM, Hitesh Shah <hitesh@apache.org> wrote:
>>>> Thanks for the suggestions, Chris. Filed TEZ-2168 for this.
>>>> At this point, I am inclined to follow option 2 mainly to retain the
>> ability for users to compile against hadoop 2.4. I am not sure if there is
>> a simple and performant way ( without using reflection for all 2.6 specific
>> calls ) to retain compile compatibility with option 1.
>>>> Any other comments for other folks on this issue in general or on the 2
>> options that Chris suggested?
>>>> thanks
>>>> — Hitesh
>>>> On Feb 26, 2015, at 1:18 PM, Chris K Wensel <chris@wensel.net> wrote:
>>>>> The immediate issue is having two mutually exclusive artifacts:
>> tez-yarn-timeline-history and tez-yarn-timeline-history
>>>>> outside of ATSHistoryACLPolicyManager, the code is identical. just the
>> dependencies are changed.
>>>>> TezClient attempts to load this Manager, under the assumption if it
>> exists, it is running on hadoop 2.6. (running on 2.4 is fatal)
>>>>> My recommendation would be never to change artifact names (or
>> conditionally choose them) inside of major releases, but accreting new,
>> optional, ones as versions progress is fine.
>>>>> thus I would either:
>>>>> create a single artifact tez-yarn-timeline-history compiled with a
>> default dep of hadoop 2.6, that includes the Manager. update the TezClient
>> code to gracefully fail if the Manager is not applicable (the runtime env
>> is Hadoop 2.4).
>>>>> or
>>>>> offer tez-yarn-timeline-history-with-acls as an optional artifact for
>> Hadoop 2.6 deployments, with the single Manager class in it, which in turn
>> requires the tez-yarn-timeline-history artifact -- which is sufficient for
>> a 2.4 runtime. if the user provides the additional -with-acls artifact,
>> they are knowingly going to have problems on Hadoop 2.4.
>>>>> I prefer the first as it keeps my build file simple. graceful
>> degradation of services per environment (with appropriate logging) is a
>> well accepted practice.
>>>>> and you can now test Tez across multiple versions Hadoop/Yarn at
>> runtime (outside of compile time).
>>>>> we do this with Cascading, just simple build file modifications to
>> verify binary compatibility (vendors fork this repo to verify their
>> distributions, and been known to find critical bugs):
>>>>> https://github.com/Cascading/cascading.compatibility
>>>>> ckw
>>>>>> On Feb 26, 2015, at 11:03 AM, Hitesh Shah <hitesh@apache.org>
>>>>>> Hi folks,
>>>>>> Chris raised a good point earlier in terms of publishing jars for
>> against different versions of hadoop. For the most part, I think we have
>> done well to ensure that the user-facing modules are version agnostic but
>> the same does not hold for other modules which are times are needed by
>> other applications for testing.
>>>>>> There aren’t really too many different options we can try.  The
>> simplest option I can think of is just to build tez against different
>> versions of hadoop with the tez.version set to something along the lines of
>> “tez.version-hadoop.version”. This would imply having
>> tez-api-0.6.0-hadoop2.4 or tez-api-0.6.0-hadoop26. For a usability point of
>> view, depending on the option we pick, users will need to switch their
>> dependencies to point to an appropriate version based on what version of
>> hadoop they are using. For apps such as hive and pig, they will need to
>> manage picking a particular version of tez based on which hadoop profile
>> they are building against.
>>>>>> Any other suggestions for publishing version dependent jars?
>>>>>> For binary releases, should we release only the minimal tarball?
>> both the minimal and full tar balls? The full tarball is the recommended
>> deployment model as it is more robust towards compatibility on a changing
>> cluster. It should work in most scenarios as long as the hadoop client
>> libraries that Tez depends on are compatible with the servers running on
>> the cluster.
>>>>>> General questions for the community/past release managers:
>>>>>> - Should we retain the simple version ( i.e. plain only x.y.z ) when
>> building against the default version of hadoop as determined by Tez? This
>> “default.version” will have a tendency to evolve over time :) . These
>> simple version jars would be in addition to the version specific jars.
>>>>>> - What versions of hadoop should we compile against? 2.2, 2.4 and
>> or 2.2,2.3,2.4,2.5,2.6 ? Please note that I am ignoring the minor version
>> so we should pick the latest version in each line i.e. 2.2.1 over 2.2.0 if
>> 2.2.1 exists.
>>>>>> Any other comments?
>>>>>> thanks
>>>>>> — Hitesh
>>>>> —
>>>>> Chris K Wensel
>>>>> chris@wensel.net
>>> —
>>> Chris K Wensel
>>> chris@wensel.net

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