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From Daniel Templeton <dan...@cloudera.com>
Subject Re: When are incompatible changes acceptable (HDFS-12990)
Date Tue, 09 Jan 2018 04:32:59 GMT
The intent of the compat guidelines is to prevent developers from making 
incompatible "improvements" at inconvenient times.  The guidelines offer 
some wiggle room for the cases where something truly broken is being 
fixed, especially for the sake of compatibility.  I would say that in 
this case, making the change is the right thing to do, but there needs 
to be a plan for how to deal with the fact that the 3.0.0 release will 
forever be an odd outlier with respect to NN ports.


On 1/8/18 8:28 PM, Aaron T. Myers wrote:
> Thanks a lot for the response, Larry. Comments inline.
> On Mon, Jan 8, 2018 at 6:44 PM, larry mccay <lmccay@apache.org> wrote:
>> Question...
>> Can this be addressed in some way during or before upgrade that allows it
>> to only affect new installs?
>> Even a config based workaround prior to upgrade might make this a change
>> less disruptive.
>> If part of the upgrade process includes a step (maybe even a script) to
>> set the NN RPC port explicitly beforehand then it would allow existing
>> deployments and related clients to remain whole - otherwise it will uptake
>> the new default port.
> Perhaps something like this could be done, but I think there are downsides
> to anything like this. For example, I'm sure there are plenty of
> applications written on top of Hadoop that have tests which hard-code the
> port number. Nothing we do in a setup script will help here. If we don't
> change the default port back to what it was, these tests will likely all
> have to be updated.
>> Meta note: we shouldn't be so pedantic about policy that we can't back out
>> something that is considered a bug or even mistake.
> This is my bigger point. Rigidly adhering to the compat guidelines in this
> instance helps almost no one, while hurting many folks.
> We basically made a mistake when we decided to change the default NN port
> with little upside, even between major versions. We discovered this very
> quickly, and we have an opportunity to fix it now and in so doing likely
> disrupt very, very few users and downstream applications. If we don't
> change it, we'll be causing difficulty for our users, downstream
> developers, and ourselves, potentially for years.
> Best,
> Aaron

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