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https://issues.apache.org/jira/browse/HDFS-12990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16325472#comment-16325472
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Eric Yang commented on HDFS-12990:
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[~chris.douglas] There are plenty of times that Hadoop code change failed with
10+ year convention because we rationalized into believing that no harm will be
done by the change. For example, CRC32C as default checksum was introduced in
a minor release, and caused people to unable to rollback during upgrade fails.
Datanode layoutVersion mismatch between Hadoop 2.0.5 to 2.2.0 releases. There
are plenty of time that things don't go as planned. We get over it by working
on the problem instead of reverting it. Many customers clusters were caught by
surprise when incompatible changes were introduced in minor or maintenance
releases. Any good change takes time and planning. I am not certain this NN
RPC change in short window can restore order as quickly as anyone have hoped.
I also don't like the port number, but I don't like the risk that someone might
be testing Hadoop 3.0.0 release, and decided to put 3.0.1 on production at
random future time to find that that we made an incompatible change for NN rpc
in a future event that we can not predict. For Hadoop 3.0.0 release to stick
out like a sore thumb is not a good way to address this issue.
> Change default NameNode RPC port back to 8020
> ---------------------------------------------
>
> Key: HDFS-12990
> URL: https://issues.apache.org/jira/browse/HDFS-12990
> Project: Hadoop HDFS
> Issue Type: Task
> Components: namenode
> Affects Versions: 3.0.0
> Reporter: Xiao Chen
> Assignee: Xiao Chen
> Priority: Critical
> Attachments: HDFS-12990.01.patch
>
>
> In HDFS-9427 (HDFS should not default to ephemeral ports), we changed all
> default ports to ephemeral ports, which is very appreciated by admin. As part
> of that change, we also modified the NN RPC port from the famous 8020 to
> 9820, to be closer to other ports changed there.
> With more integration going on, it appears that all the other ephemeral port
> changes are fine, but the NN RPC port change is painful for downstream on
> migrating to Hadoop 3. Some examples include:
> # Hive table locations pointing to hdfs://nn:port/dir
> # Downstream minicluster unit tests that assumed 8020
> # Oozie workflows / downstream scripts that used 8020
> This isn't a problem for HA URLs, since that does not include the port
> number. But considering the downstream impact, instead of requiring all of
> them change their stuff, it would be a way better experience to leave the NN
> port unchanged. This will benefit Hadoop 3 adoption and ease unnecessary
> upgrade burdens.
> It is of course incompatible, but giving 3.0.0 is just out, IMO it worths to
> switch the port back.
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