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https://issues.apache.org/jira/browse/HDFS-4820?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13662466#comment-13662466
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Chris Nauroth commented on HDFS-4820:
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{quote}
This does sound problematic. Should users really care if the configuration
object is populated with a lot of defaults (not all defaults unless we've been
extremely careful about putting all keys into *-default.xml).
In terms of the values being used by client being the same across versions -
changing defaults within a major release will likely be incompatible,
especially for user facing keys - and we should avoid this.
{quote}
I think the biggest compatibility concern would be publishing a change such
that getting a particular key used to return a default, but now it returns
null. The surrounding application code that gets that key might not be
null-safe. Granted, the non-defaulting {{Configuration#get}} documentation
says that it could return null, so we haven't set ourselves up with a contract
that we must handle this gracefully. However, some callers might assume that
extremely basic things like dfs.replication are always going to be defined, so
getting a null would be a nasty surprise.
BTW, just so it's clear, I'm not necessarily opposed to the change. I just
wanted to share some concerns that would likely force us to flag the change as
backwards-incompatible.
> Remove hdfs-default.xml
> -----------------------
>
> Key: HDFS-4820
> URL: https://issues.apache.org/jira/browse/HDFS-4820
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.0.4-alpha
> Reporter: Siddharth Seth
>
> Similar to YARN-673, which contains additional details.
> There's separate jiras for YARN, MR and HDFS so enough people take a look.
> Looking for reasons for these files to exist, other than the ones mentioned
> in YARN-673, or a good reason to keep the files.
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