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https://issues.apache.org/jira/browse/HADOOP-928?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12468456
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Doug Cutting commented on HADOOP-928:
-------------------------------------
> keep all the raw methods in the FileSystem interface
> DistributedFileSystem and LocalFileSystem extend ChecksumFileSystem and
> implement all the raw methods
I think we only need to keep the raw methods if you intend to subclass to add
checksums. If instead, ChecksumFileSystem wraps another FileSystem, then one
can do something like:
class RawHDFS extends FileSystem {
public RawHDFS() { ... }
.. implement open, create, list, etc. ...
}
abstract class ChecksumFS extends FilteredFileSystem {
public ChecksumFS(FileSystem fs) { super(fs); }
.. implement open, create, list, etc. ...
}
class ChecksumHDFS extends ChecksumFileSystem {
public ChecksumHDFS() { super(new RawHDFS()); }
}
Does that make sense? But perhaps you prefer to subclass for some reason? I
like the wrapper based approach primarily because it eliminates all the 'raw'
methods.
> make checksums optional per FileSystem
> --------------------------------------
>
> Key: HADOOP-928
> URL: https://issues.apache.org/jira/browse/HADOOP-928
> Project: Hadoop
> Issue Type: Improvement
> Components: fs
> Reporter: Doug Cutting
> Assigned To: Hairong Kuang
>
> Checksumming is currently built into the base FileSystem class. It should
> instead be optional, with each FileSystem implementation electing whether to
> use the Hadoop-provided checksum system, or to disable it, or to implement
> its own custom checksum system.
> To implement this, a ChecksumFileSystem implementation can be provided that
> wraps another FileSystem implementation, implementing checksums as in
> Hadoop's current mandatory implementation (i.e., as a separate crc file per
> file that's elided from directory listings). The 'raw' FileSystem methods
> would be removed. FSDataInputStream and FSDataOutputStream would be made
> interfaces.
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