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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10047) Allow Compressor/Decompressor APIs to expose a Direct ByteBuffer API
Date Tue, 15 Oct 2013 18:04:42 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13795446#comment-13795446
] 

Chris Nauroth commented on HADOOP-10047:
----------------------------------------

Thanks for filing this, [~gopalv].  From the Javadocs, it looks like you prototyped this for
the zlib compressor and decompressor.  When you get a chance, it would be nice if you could
post that so we can get a sense for what this looks like in implementing classes, even if
it's not a final patch.

One of our goals in HDFS-5191 was to achieve an API that didn't require the caller to write
different code for direct vs. non-direct.  Unfortunately, I don't see a way to achieve that
here.  In the input streams, we had the advantage of an abstract base class where we could
put a default fallback copying implementation.  {{Compressor}} and {{Decompressor}} are interfaces,
so we can't put in a default implementation, and we also can't add the new methods without
breaking backwards-compatibility.  It seems inevitable that callers will have to downcast
to {{DirectCompressor}}/{{DirectDecompressor}}.  I don't see another way.

> Allow Compressor/Decompressor APIs to expose a Direct ByteBuffer API
> --------------------------------------------------------------------
>
>                 Key: HADOOP-10047
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10047
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: io
>            Reporter: Gopal V
>            Assignee: Gopal V
>              Labels: compression
>         Attachments: DirectCompressor.html, DirectDecompressor.html
>
>
> With the Zero-Copy reads in HDFS (HDFS-5260), it becomes important to perform all I/O
operations without copying data into byte[] buffers or other buffers which wrap over them.
> This is a proposal for adding new DirectCompressor and DirectDecompressor interfaces
to the io.compress, to indicate codecs which want to surface the direct buffer layer upwards.
> The implementation may or may not copy the buffers passed in, but should work with direct
heap/mmap buffers and cannot assume .array() availability.



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