Hello Pulsar community, I would like to start a discussion about Java 11 support and about dropping support for JDK8 on the server side. It will take time, see my points below.
At the moment we have these use cases about Java compatibility: - Java client users - Building Pulsar and running Pulsar tests - Server users that use the binary tarball - Apache Pulsar Docker images consumers I have been running in production BookKeeper and Pulsar on modern JDKs (Java version > 8) for much time and I see that there are no issues at least for the scenarios I have seen. JDK11 is currently referred to as LTS by major vendors (for whatever it means, please do not enter a "Java LTS thread", there are plenty of threads about what is Java LTS about) and Java 17 is coming. I expect that any of the new users will start running on JDK11 (and probably on JDK15 for the early adopters) if they do not want to pay for JDK8 support Also the latest versions of Presto require Java 11 to run, if we do not move to Java 11 we won't be able to upgrade Presto. This is what I expect on the mid term (after 2.8): 1) Java Clients: stick to JDK8 compatibility I believe that on the Java client side we should stick to JDK8 compatibility, because unfortunately JDK8 is still a version that is widely used in the industry. In order to ensure JDK8 compatibility we have useful tools: - there are Maven plugin that ensure that we are not producing and consuming third party libraries that are not compatible with JDK8 - we can add one (or more) Maven modules that run on CI using JDK8 and consume the artifacts produced by the build 2) Building Pulsar and running Tests We can require Pulsar to be built on JDK11. We can set maven.compiler.release to 11 in generale and maven.compiler.release to 8 for all of the modules that concur to build up the Java client Tests will run on JDK11 on CI. We could desire to run the Pulsar client tests on JDK8, but many of them are indeed inside the pulsar-broker module. 3) Server users that use the binary tarball We will have to announce that from Pulsar 2.x (2.8 or 2.9?) Pulsar server side components will require JDK11 The same applies to users that run Pulsar broker by starting it from the Jars deployed to Maven central. 4) Docker images consumers: This is easy, just change the images in order to use JDK11. I believe that enforcing JDK11 on the server side side is a big move and we should announce it with care and let users prepare for this jump. So in the meantime we could start with a soft transition plan, starting for 2.8 release: - Build Pulsar on JDK11 and run CI on JDK11 - Set maven.compiler.release to JDK8 - Change docker images to JDK11 This way: - consumers of the Java client will be able to run on JDK8 - consumers of the Binary tarballs for the server will be able to run on JDK8, say for Pulsar 2.8 - consumers of Docker images will start to enjoy JDK11 - Pulsar developers will get used to having JDK11, but they won't be able to leverage JDK11 language and JRE features (only faster runtime, GC....) I can start a PIP, but I believe a little discussion on the ML is a good starting point. Thoughts ? Enrico
