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From Allen Wittenauer ...@effectivemachines.com>
Subject Re: [Release thread] 2.6.5 release activities
Date Mon, 15 Aug 2016 17:55:50 GMT

> On Aug 12, 2016, at 8:19 AM, Junping Du <jdu@hortonworks.com> wrote:
>  In this community, we are so aggressive to drop Java 7 support in 3.0.x release. Here,
why we are so conservative to keep releasing new bits to support Java 6?

	I don't view a group of people putting bug fixes into a micro release as particularly conservative.
 If a group within the community wasn't interested in doing it, 2.6.5 wouldn't be happening.

	But let's put the releases into context, because I think it tells a more interesting story.

		* hadoop 2.6.x = EOLed JREs (6,7) 
		* hadoop 2.7 -> hadoop 2.x = transitional (7,8)
		* hadoop 3.x = JRE 8
		* hadoop 4.x = JRE 9 

	There are groups of people still using JDK6 and they want bug fixes in a maintenance release.
 Boom, there's 2.6.x.

	Hadoop 3.x has been pushed off for years for "reasons".  So we still have releases coming
off of branch-2.  If 2.7 had been released as 3.x, this chart would look less weird. But it
wasn't thus 2.x has this weird wart in the middle of that supports JDK7 and JDK8.  Given the
public policy and roadmaps of at least one major vendor at the time of this writing, we should
expect to see JDK7 support for at least the next two years after 3.x appears. Bang, there's
2.x, where x is some large number.

	Then there is the future.  People using JRE 8 want to use newer dependencies.  A reasonable
request. Some of these dependency updates won't work with JRE 7.   We can't do that in hadoop
2.x in any sort of compatible way without breaking the universe. (Tons of JIRAs on this point.)
This means we can only do it in 3.x (re: Hadoop Compatibility Guidelines).  Kapow, there's

	The log4j community has stated that v1 won't work with JDK9. In turn, this means we'll need
to upgrade to v2 at some point.  Upgrading to v2 will break the log4j properties file (and
maybe other things?). Another incompatible change and it likely won't appear until Apache
Hadoop v4 unless someone takes the initiative to fix it before v3 hits store shelves.  This
makes JDK9 the likely target for Apache Hadoop v4.  

	Having major release cadences tied to JRE updates isn't necessarily a bad thing and definitely
forces the community to a) actually stop beating around the bush on majors and b) actually
makes it relatively easy to determine what the schedule looks like to some degree.

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