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[ https://issues.apache.org/jira/browse/HADOOP-928?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12468456 ]

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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postedJan 25, '07 at 4:19a
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