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From Vinod Kumar Vavilapalli <vino...@hortonworks.com>
Subject Re: Looking to a Hadoop 3 release
Date Sat, 07 Mar 2015 00:32:58 GMT
I'd encourage everyone to post their wish list on the Roadmap wiki that *warrants* making incompatible
changes forcing us to go 3.x.

+1 to Jason's comments on general. We can keep rolling alphas that downstream can pick up,
but I'd also like us to clarify the exit criterion for a GA release of 3.0 and its relation
to the life of 2.x if we are going this route. This brings us back to the roadmap discussion,
and a collective agreement about a logical step at a future point in time where we say we
have enough incompatible features in 3.x that we can stop putting more of them and start stabilizing

Irrespective of that, here is my proposal in the interim:
 - Run JDK7 + JDK8 first in a compatible manner like I mentioned before for atleast two releases
in branch-2: say 2.8 and 2.9 before we consider taking up the gauntlet on 3.0.
 - Continue working on the classpath isolation effort and try making it as compatible as is
possible for users to opt in and migrate easily.


On Mar 5, 2015, at 1:44 PM, Jason Lowe <jlowe@yahoo-inc.com.INVALID> wrote:

> I'm OK with a 3.0.0 release as long as we are minimizing the pain of maintaining yet
another release line and conscious of the incompatibilities going into that release line.
> For the former, I would really rather not see a branch-3 cut so soon.  It's yet another
line onto which to cherry-pick, and I don't see why we need to add this overhead at such an
early phase.  We should only create branch-3 when there's an incompatible change that the
community wants and it should _not_ go into the next major release (i.e.: it's for Hadoop
4.0).  We can develop 3.0 alphas and betas on trunk and release from trunk in the interim.
 IMHO we need to stop treating trunk as a place to exile patches.
> For the latter, I think as a community we need to evaluate the benefits of breaking compatibility
against the costs of migrating.  Each time we break compatibility we create a hurdle for people
to jump when they move to the new release, and we should make those hurdles worth their time.
 For example, wire-compatibility has been mentioned as part of this.  Any feature that breaks
wire compatibility better be absolutely amazing, as it creates a huge hurdle for people to
> To summarize:+1 for a community-discussed roadmap of what we're breaking in Hadoop 3
and why it's worth it for users
> -1 for creating branch-3 now, we can release from trunk until the next incompatibility
for Hadoop 4 arrives
> +1 for baking classpath isolation as opt-in on 2.x and eventually default on in 3.0
> Jason
>      From: Andrew Wang <andrew.wang@cloudera.com>
> To: "hdfs-dev@hadoop.apache.org" <hdfs-dev@hadoop.apache.org> 
> Cc: "common-dev@hadoop.apache.org" <common-dev@hadoop.apache.org>; "mapreduce-dev@hadoop.apache.org"
<mapreduce-dev@hadoop.apache.org>; "yarn-dev@hadoop.apache.org" <yarn-dev@hadoop.apache.org>

> Sent: Wednesday, March 4, 2015 12:15 PM
> Subject: Re: Looking to a Hadoop 3 release
> Let's not dismiss this quite so handily.
> Sean, Jason, and Stack replied on HADOOP-11656 pointing out that while we
> could make classpath isolation opt-in via configuration, what we really
> want longer term is to have it on by default (or just always on). Stack in
> particular points out the practical difficulties in using an opt-in method
> in 2.x from a downstream project perspective. It's not pretty.
> The plan that both Sean and Jason propose (which I support) is to have an
> opt-in solution in 2.x, bake it there, then turn it on by default
> (incompatible) in a new major release. I think this lines up well with my
> proposal of some alphas and betas leading up to a GA 3.x. I'm also willing
> to help with 2.x release management if that would help with testing this
> feature.
> Even setting aside classpath isolation, a new major release is still
> justified by JDK8. Somehow this is being ignored in the discussion. Allen,
> historically the voice of the user in our community, just highlighted it as
> a major compatibility issue, and myself and Tucu have also expressed our
> very strong concerns about bumping this in a minor release. 2.7's bump is a
> unique exception, but this is not something to be cited as precedent or
> policy.
> Where does this resistance to a new major release stem from? As I've
> described from the beginning, this will look basically like a 2.x release,
> except for the inclusion of classpath isolation by default and target
> version JDK8. I've expressed my desire to maintain API and wire
> compatibility, and we can audit the set of incompatible changes in trunk to
> ensure this. My proposal for doing alpha and beta releases leading up to GA
> also gives downstreams a nice amount of time for testing and validation.
> Regards,
> Andrew
> On Tue, Mar 3, 2015 at 2:32 PM, Arun Murthy <acm@hortonworks.com> wrote:
>> Awesome, looks like we can just do this in a compatible manner - nothing
>> else on the list seems like it warrants a (premature) major release.
>> Thanks Vinod.
>> Arun
>> ________________________________________
>> From: Vinod Kumar Vavilapalli <vinodkv@hortonworks.com>
>> Sent: Tuesday, March 03, 2015 2:30 PM
>> To: common-dev@hadoop.apache.org
>> Cc: hdfs-dev@hadoop.apache.org; mapreduce-dev@hadoop.apache.org;
>> yarn-dev@hadoop.apache.org
>> Subject: Re: Looking to a Hadoop 3 release
>> I started pitching in more on that JIRA.
>> To add, I think we can and should strive for doing this in a compatible
>> manner, whatever the approach. Marking and calling it incompatible before
>> we see proposal/patch seems premature to me. Commented the same on JIRA:
>> https://issues.apache.org/jira/browse/HADOOP-11656?focusedCommentId=14345875&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14345875
>> .
>> Thanks
>> +Vinod
>> On Mar 2, 2015, at 8:08 PM, Andrew Wang <andrew.wang@cloudera.com<mailto:
>> andrew.wang@cloudera.com>> wrote:
>> Regarding classpath isolation, based on what I hear from our customers,
>> it's still a big problem (even after the MR classloader work). The latest
>> Jackson version bump was quite painful for our downstream projects, and the
>> HDFS client still leaks a lot of dependencies. Would welcome more
>> discussion of this on HADOOP-11656, Steve, Colin, and Haohui have already
>> chimed in.

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