Hello all, Over in HDFS-12990 <https://issues.apache.org/jira/browse/HDFS-12990>[1], we're having some discussion about whether or not it's ever acceptable to make an incompatible change in a minor or dot release. In general this is of course undesirable and should be avoided in almost all cases. However, I believe that each instance of someone desiring to make an incompatible change should be evaluated on a case-by-case basis to consider the costs and benefits of making that change. For example, I believe that we've historically made incompatible changes in minor or dot releases which would break older clients for security reasons.
In this particular case linked above, I believe that given that Hadoop 3.0.0 was just released, and thus very few folks are likely to have deployed it, it would benefit a large number of existing deployments and downstream applications to change the default NN RPC port number back to what it was in all previously-released versions of Apache Hadoop. I'd like to make this change in 3.0.1, and there is no question that doing so would should be considered an incompatible change between 3.0.0 and 3.0.1. However, I believe this incompatible change is warranted given the circumstances. Would like to hear others' thoughts on this. Thanks, Aaron [1] For some background, it used to be the case that many of Hadoop's default service ports were in the ephemeral range. This could potentially cause a service to fail to start up on a given host if some other process had happened to have already bound to said port. As part of that effort, we also changed the default NN RPC port from 8020 to 9820. Even though 8020 wasn't in the ephemeral range, we moved it to 9820 to be close to the new range of the rest of the ports. At the time this change was made, though, I and others didn't realize the substantial downsides that doing so would introduce, for example the Hive metastore will put full HDFS paths including the port into its database, which can be a substantial upgrade headache.
