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From Vinod Kumar Vavilapalli <vino...@hortonworks.com>
Subject Re: Looking to a Hadoop 3 release
Date Tue, 03 Mar 2015 02:46:33 GMT
Agreed. The difference between a 3.0 GA release and a parallel 2.x release line is just JDK8
+ a different classpath (potentially isolated) - doesn't sound like a big enough delta warranting
the license to break compat.

Thanks,
+Vinod

On Mar 2, 2015, at 6:30 PM, Arun Murthy <acm@hortonworks.com> wrote:

> Andrew,
> 
> Thanks for bringing up this discussion.
> 
> I'm a little puzzled for I feel like we are rehashing the same discussion from last year
- where we agreed on a different course of action w.r.t switch to JDK7.
> 
> IAC, breaking compatibility for hadoop-3 is a pretty big cost - particularly for users
such as Yahoo/Twitter/eBay who have several clusters between which compatibility is paramount.

> 
> Now, breaking compatibility is perfectly fine over time where there is sufficient benefit
e.g. HDFS HA or YARN in hadoop-2 (v/s hadoop-1). 
> 
> However, I'm struggling to quantify the benefit of hadoop-3 for users for the cost of
the breakage.
> 
> Given that we already agreed to put in JDK7 in 2.7, and that the classpath is a fairly
minor irritant given some existing solutions (e.g. a new default classloader), how do you
quantify the benefit for users?
> 
> We could just do JDK8 in hadoop-2.10 or some such, you are definitely welcome to run
the RM role for that release.
> 
> Furthermore, I'm really concerned that this will be used as an opportunity to further
break compat in more egregious ways. 
> 
> Also, are you foreseeing more compat breaks? OTOH, if we all agree that we should absolutely
prevent compat breakages such as the client-server wire protocol, I feel the point of a major
release is kinda lost.
> 
> Overall, my biggest concern is the compatibility story vis-a-vis the benefit. 
> 
> Thoughts?
> 
> thanks,
> Arun
> 
> ________________________________________
> From: Andrew Wang <andrew.wang@cloudera.com>
> Sent: Monday, March 02, 2015 3:19 PM
> To: common-dev@hadoop.apache.org; mapreduce-dev@hadoop.apache.org; hdfs-dev@hadoop.apache.org;
yarn-dev@hadoop.apache.org
> Subject: Looking to a Hadoop 3 release
> 
> Hi devs,
> 
> It's been a year and a half since 2.x went GA, and I think we're about due
> for a 3.x release.
> Notably, there are two incompatible changes I'd like to call out, that will
> have a tremendous positive impact for our users.
> 
> First, classpath isolation being done at HADOOP-11656, which has been a
> long-standing request from many downstreams and Hadoop users.
> 
> Second, bumping the source and target JDK version to JDK8 (related to
> HADOOP-11090), which is important since JDK7 is EOL in April 2015 (two
> months from now). In the past, we've had issues with our dependencies
> discontinuing support for old JDKs, so this will future-proof us.
> 
> Between the two, we'll also have quite an opportunity to clean up and
> upgrade our dependencies, another common user and developer request.
> 
> I'd like to propose that we start rolling a series of monthly-ish series of
> 3.0 alpha releases ASAP, with myself volunteering to take on the RM and
> other cat herding responsibilities. There are already quite a few changes
> slated for 3.0 besides the above (for instance the shell script rewrite) so
> there's already value in a 3.0 alpha, and the more time we give downstreams
> to integrate, the better.
> 
> This opens up discussion about inclusion of other changes, but I'm hoping
> to freeze incompatible changes after maybe two alphas, do a beta (with no
> further incompat changes allowed), and then finally a 3.x GA. For those
> keeping track, that means a 3.x GA in about four months.
> 
> I would also like to stress though that this is not intended to be a big
> bang release. For instance, it would be great if we could maintain wire
> compatibility between 2.x and 3.x, so rolling upgrades work. Keeping
> branch-2 and branch-3 similar also makes backports easier, since we're
> likely maintaining 2.x for a while yet.
> 
> Please let me know any comments / concerns related to the above. If people
> are friendly to the idea, I'd like to cut a branch-3 and start working on
> the first alpha.
> 
> Best,
> Andrew


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