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https://issues.apache.org/jira/browse/HDFS-4820?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13660852#comment-13660852
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Chris Nauroth commented on HDFS-4820:
-------------------------------------
Removing *-default.xml seems to complicate resolution of some of our more
dynamic configuration properties. A good example is our mapping of file system
impl classes by URI scheme used by {{AbstractFileSystem#createFileSystem}}:
{code}
<property>
<name>fs.AbstractFileSystem.file.impl</name>
<value>org.apache.hadoop.fs.local.LocalFs</value>
<description>The AbstractFileSystem for file: uris.</description>
</property>
<property>
<name>fs.AbstractFileSystem.hdfs.impl</name>
<value>org.apache.hadoop.fs.Hdfs</value>
<description>The FileSystem for hdfs: uris.</description>
</property>
{code}
{code}
public static AbstractFileSystem createFileSystem(URI uri, Configuration conf)
throws UnsupportedFileSystemException {
Class<?> clazz = conf.getClass("fs.AbstractFileSystem." +
uri.getScheme() + ".impl", null);
if (clazz == null) {
throw new UnsupportedFileSystemException(
"No AbstractFileSystem for scheme: " + uri.getScheme());
}
return (AbstractFileSystem) newInstance(clazz, uri, conf);
}
{code}
Without defaults in the XML, this code will need to hard-code the mapping
somewhere. We'll have to remember to cover all cases like this.
{quote}
...it should not be part of the jar and should not be looked for and loaded in
by default into the Configuration object.
{quote}
This may be a bigger concern for compatibility. {{Configuration}} is annotated
public/stable, and I've seen a lot of tutorials with sample code that
instantiates a new instance and expects it to be fully populated with the keys
from *-default.xml. For full compatibility, I suppose we'd need to update not
only our own {{Configuration#get}} calls to enforce the defaults, but also
guarantee that if a client creates a new instance, they get the same values
that used to be provided in the XML. Again, this probably would involve some
kind of hard-coding during static initialization.
> 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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