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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-928) make checksums optional per FileSystem
Date Thu, 22 Feb 2007 20:43:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-928?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12475156
] 

Doug Cutting commented on HADOOP-928:
-------------------------------------

> return a (unbuffered) FSDataInputStream for open(f) and a BufferedFSDataInputStream for
open(f, bufferSize)

I'm not convinced we should ever return an unbuffered stream.  I think the open(f) call should
return a stream with the default buffer size.  Note that writes that are larger than the buffer
bypass the buffer, so applications that layer their own buffers on top don't pay a penalty
when using a buffered stream.  They might instead however use open(f, bufferSize), specifying
a small buffer size, to save memory.

Note also that a RAM-based FileSystem might disable buffering altogether--even when a bufferSize
is specified.

> 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
>         Attachments: checksum.patch
>
>
> 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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