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From Mohit Sabharwal <mo...@cloudera.com>
Subject [discuss] jdk8 support
Date Fri, 08 Apr 2016 23:34:50 GMT
Hi folks,

Oracle EOL'ed (ended public updates) for Java 7 in April 2015.
In order to support Java 8, we fixed quite a bunch of tests in
HIVE-8607 (*) early last year. However, since our pre-commit tests run
on JDK7 only, any JDK8 test failures are getting ignored. As a result,
the count has crept up
<http://ec2-174-129-184-35.compute-1.amazonaws.com/jenkins/job/HIVE-TRUNK-JAVA8/>
back
from zero to 125.

Some options to address this:

(1) Run pre-commit tests on both JDK7 and JDK8, in both 1.x
and 2.x: This will further slow down the pre-commit run.

(2) Alternate pre-commit test runs between JDK7 and JDK8 (in
both 1.x and 2.x): It's a cheap hack. More messy, though failures
won't get ignored.

(3) Drop support for JDK7 in Hive 2.x, i.e. build and test Hive 2.x on
JDK8 only. For Hive 1.x, continue running JDK7 pre-commit tests.
The pros are:
- Simple test matrix.
- No need to slow down test run or maintain version specific golden files
(**).
- 2.x looks like the logical place to move to JDK8.
- Users transitioning to JDK8 for all other services do not have to
maintain
multiple java versions on the cluster.

Option (3) looks most attractive to me.

Moving to JDK8 also lines us up better for Java 9, which is on the
horizon (Oracle will end public updates for Java 8 in Sep 2017)

Around 100 of the latest crop of failures are due to one cause
(HIVE-13409).
I can take a pass at triaging the rest if there is consensus around what
to do overall.

Thanks,
Mohit

(*) Most test failures are due to JDK8 using a different hash function for
HashMap  compared to JDK7. This results in (mostly benign, but hard
to debug) ordering differences in q-file output related to serialization
order of map entries, numbering of stages in query plan, etc.

(**) In some cases, hash function related ordering differences originate
in external libraries like Avro, antlr, json ,Thrift's map, etc. for which
code
changes are either more involved or led to more test failures.  To address
this,
we added support for version specific golden files (HIVE-9109). Currently,
there
are ~40 golden files with ".java1.8.out" extension.

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