> On Aug 12, 2016, at 8:19 AM, Junping Du <j...@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 3.x
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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