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From "Chris Douglas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3646) Providing bzip2 as codec
Date Wed, 09 Jul 2008 19:51:31 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3646?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12612247#action_12612247

Chris Douglas commented on HADOOP-3646:

A few nits:
* Please remove the {{//...............}} and {{//*****//}} comments completely or replace
them with meaningful javadoc
* FeatureNotImplemented Exception can be replaced with UnsupportedOperationException
* WrongBZip2Header can be replaced by an IOException with a meaningful description
* Several close() methods contain commented-out code
* Instead of returning null for methods like create(De|C)ompressor, throwing UnsupportedOperationException
is preferred.
* createInputStream and createOutputStream in Bzip2Codec should not simply ignore the Decompressor/Compressor,
but throw an exception. This isn't really a problem- since one can't obtain these from the
codec- but it's worth fixing.
* createInputStream should not swallow the exception; changing WrongBZip2Header to an IOException
should remove the need for this, anyway
* The change to CompressionCodecFactory should be reverted; it's sufficient to add Bzip2Codec
to the config

I tried running wordcount on some sample bzip text and this worked perfectly.

> Providing bzip2 as codec
> ------------------------
>                 Key: HADOOP-3646
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3646
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: conf, io
>    Affects Versions: 0.19.0
>            Reporter: Abdul Qadeer
>             Fix For: 0.19.0
>         Attachments: HADOOP-3646.patch
>   Original Estimate: 1008h
>  Remaining Estimate: 1008h
> Hadoop recognizes gzip compressed input and automatically decompresses the data before
providing it to the mapper. But Hadoop can not split a gzip stream due to the very nature
of the gzip compression. Consequently one gzip stream (e.g a whole file) can go to only one
mapper.  On the contrary Bzip2 compressed stream can be split across its block delimiters.
> We are interested in extending Hadoop to support splittable bzip2 with a codec.  (https://issues.apache.org/jira/browse/HADOOP-1823
 uses input reader to split the bzip2 files, which must be provided by the user and can handle
FileInputFormat.  If a user wants to use some other input format or wants to do custom record
handling, he must write a new input reader!)
> We have a patch now that provides a basic bzip2 codec equivalent to the current gzip
codec.  We are in the process of extending that to support splitting.

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