On 5 Apr 2018, at 18:04, Matei Zaharia <matei.zaha...@gmail.com<mailto:matei.zaha...@gmail.com>> wrote:
Java 9/10 support would be great to add as well. Be aware that the work moving hadoop core to java 9+ is still a big piece of work being undertaken by Akira Ajisaka & colleagues at NTT https://issues.apache.org/jira/browse/HADOOP-11123 Big dependency updates and handling Oracle hiding sun.misc stuff which low level code depends on are the troublespots, with a move to Log4J 2 going to be observably traumatic to all apps which require a log4.properties to set themselves up. As usual: any testing which can be done early will be welcomed by all, the earlier the better That stuff is all about getting things working: supporting the java 9 packaging model. Which is a really compelling reason to go for it Regarding Scala 2.12, I thought that supporting it would become easier if we change the Spark API and ABI slightly. Basically, it is of course possible to create an alternate source tree today, but it might be possible to share the same source files if we tweak some small things in the methods that are overloaded across Scala and Java. I don’t remember the exact details, but the idea was to reduce the total maintenance work needed at the cost of requiring users to recompile their apps. I’m personally for moving to 3.0 because of the other things we can clean up as well, e.g. the default SQL dialect, Iterable stuff, and possibly dependency shading (a major pain point for lots of users) Hadoop 3 does have a shaded client, though not enough for Spark; if work identifying & fixing the outstanding dependencies is started now, Hadoop 3.2 should be able to offer the set of shaded libraries needed by Spark. There's always a price to that, which is in redistributable size and it's impact on start times, duplicate classes loaded (memory, reduced chance of JIT recompilation, ...), and the whole transitive-shading problem. Java 9 should be the real target for a clean solution to all of this.
