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From "Kevin J. Price (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6297) Hadoop's support for zlib library lacks support to perform flushes (Z_SYNC_FLUSH and Z_FULL_FLUSH)
Date Thu, 24 Feb 2011 02:42:38 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-6297?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998673#comment-12998673
] 

Kevin J. Price commented on HADOOP-6297:
----------------------------------------

A user creating a customized compression scheme using zlib that requires mid-compression-stream
syncing. For example, a compression method that generates fixed-sized output blocks.

> Hadoop's support for zlib library lacks support to perform flushes (Z_SYNC_FLUSH and
Z_FULL_FLUSH)
> --------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-6297
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6297
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: io
>            Reporter: Kevin J. Price
>            Assignee: Kevin J. Price
>            Priority: Minor
>         Attachments: zlibpatch-0.3.patch, zlibpatch.patch
>
>
> The zlib library supports the ability to perform two types of flushes when deflating
data. It can perform both a Z_SYNC_FLUSH, which forces all input to be written as output and
byte-aligned and resets the Huffman coding, and it also supports a Z_FULL_FLUSH, which does
the same thing but additionally resets the compression dictionary.  The Hadoop wrapper for
the zlib library does not support either of these two methods.
> Adding support should be fairly trivial.  An additional deflate method that takes a fourth
"flush" parameter, and a modification to the native c code to accept this fourth parameter
and pass it along to the zlib library.  I can submit a patch for this if desired.
> It should be noted that the native SUN Java API is likewise missing this functionality,
as has been noted for over a decade here: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4206909

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