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From Colin McCabe <cmcc...@alumni.cmu.edu>
Subject Re: Plans of moving towards JDK7 in trunk
Date Sat, 05 Apr 2014 10:53:21 GMT
I've been using JDK7 for Hadoop development for a while now, and I
know a lot of other folks have as well.  Correct me if I'm wrong, but
what we're talking about here is not "moving towards JDK7" but
"breaking compatibility with JDK6."

There are a lot of good reasons to ditch JDK6.  It would let us use
new APIs in JDK7, especially the new file APIs.  It would let us
update a few dependencies to newer versions.

I don't like the idea of breaking compatibility with JDK6 in trunk,
but not in branch-2.  The traditional reason for putting something in
trunk but not in branch-2 is that it is new code that needs some time
to prove itself.  This doesn't really apply to incrementing min.jdk--
we could do that easily whenever we like.  Meanwhile, if trunk starts
accumulating jdk7-only code and dependencies, backports from trunk to
branch-2 will become harder and harder over time.

Since we make stable releases off of branch-2, and not trunk, I don't
see any upside to this.  To be honest, I see only negatives here.
More time backporting, more issues that show up only in production
(branch-2) and not on dev machines (trunk).

Maybe it's time to start thinking about what version of branch-2 will
drop jdk6 support.  But until there is such a version, I don't think
trunk should do it.

best,
Colin


On Fri, Apr 4, 2014 at 3:15 PM, Haohui Mai <hmai@hortonworks.com> wrote:
> I'm referring to the later case. Indeed migrating JDK7 for branch-2 is more
> difficult.
>
> I think one reasonable approach is to put the hdfs / yarn clients into
> separate jars. The client-side jars can only use JDK6 APIs, so that
> downstream projects running on top of JDK6 continue to work.
>
> The HDFS/YARN/MR servers need to be run on top of JDK7, and we're free to
> use JDK7 APIs inside them. Given the fact that there're way more code in
> the server-side compared to the client-side, having the ability to use JDK7
> in the server-side only might still be a win.
>
> The downside I can think of is that it might complicate the effort of
> publishing maven jars, but this should be an one-time issue.
>
> ~Haohui
>
>
> On Fri, Apr 4, 2014 at 2:37 PM, Alejandro Abdelnur <tucu@cloudera.com>wrote:
>
>> Haohui,
>>
>> Is the idea to compile/test with JDK7 and recommend it for runtime and stop
>> there? Or to start using JDK7 API stuff as well? If the later is the case,
>> then backporting stuff to branch-2 may break and patches may have to be
>> refactored for JDK6. Given that branch-2 got GA status not so long ago, I
>> assume it will be active for a while.
>>
>> What are your thoughts on this regard?
>>
>> Thanks
>>
>>
>> On Fri, Apr 4, 2014 at 2:29 PM, Haohui Mai <hmai@hortonworks.com> wrote:
>>
>> > Hi,
>> >
>> > There have been multiple discussions on deprecating supports of JDK6 and
>> > moving towards JDK7. It looks to me that the consensus is that now hadoop
>> > is ready to drop the support of JDK6 and to move towards JDK7. Based on
>> the
>> > consensus, I wonder whether it is a good time to start the migration.
>> >
>> > Here are my understandings of the current status:
>> >
>> > 1. There is no more public updates of JDK6 since Feb 2013. Users no
>> longer
>> > get fixes of security vulnerabilities through official public updates.
>> > 2. Hadoop core is stuck with out-of-date dependency unless moving towards
>> > JDK7. (see
>> > http://hadoop.6.n7.nabble.com/very-old-dependencies-td71486.html)
>> > The implementation can also benefit from it thanks to the new
>> > functionalities in JDK7.
>> > 3. The code is ready for JDK7. Cloudera and Hortonworks have successful
>> > stories of supporting Hadoop on JDK7.
>> >
>> >
>> > It seems that the real work of moving to JDK7 is minimal. We only need to
>> > (1) make sure the jenkins are running on top of JDK7, and (2) to update
>> the
>> > minimum required Java version from 6 to 7. Therefore I propose that let's
>> > move towards JDK7 in trunk in the short term.
>> >
>> > Your feedbacks are appreciated.
>> >
>> > Regards,
>> > Haohui
>> >
>> > --
>> > CONFIDENTIALITY NOTICE
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>>
>>
>>
>> --
>> Alejandro
>>
>
> --
> CONFIDENTIALITY NOTICE
> NOTICE: This message is intended for the use of the individual or entity to
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