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https://issues.apache.org/jira/browse/HADOOP-8148?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13257983#comment-13257983
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Todd Lipcon commented on HADOOP-8148:
-------------------------------------
bq. I've been thinking about this, and here's some dust: this interface seems
to work well enough for software codecs, but for multicore hardware codecs, it
is necessary to process multiple records in parallel. To do this, the
decompression needs to start reading and decompressing data before the caller
shows up with his direct buffer.
Sorry for my ignorance in this area, but: this implies that hardware codecs are
pipelined? In the LineReader use case, you're saying you would provide a much
larger block to the codec ahead of what is being read out of the decompression
side?
> Zero-copy ByteBuffer-based compressor / decompressor API
> --------------------------------------------------------
>
> Key: HADOOP-8148
> URL: https://issues.apache.org/jira/browse/HADOOP-8148
> Project: Hadoop Common
> Issue Type: New Feature
> Components: io
> Reporter: Tim Broberg
> Assignee: Tim Broberg
> Attachments: hadoop8148.patch
>
>
> Per Todd Lipcon's comment in HDFS-2834, "
> Whenever a native decompression codec is being used, ... we generally have
> the following copies:
> 1) Socket -> DirectByteBuffer (in SocketChannel implementation)
> 2) DirectByteBuffer -> byte[] (in SocketInputStream)
> 3) byte[] -> Native buffer (set up for decompression)
> 4*) decompression to a different native buffer (not really a copy -
> decompression necessarily rewrites)
> 5) native buffer -> byte[]
> with the proposed improvement we can hopefully eliminate #2,#3 for all
> applications, and #2,#3,and #5 for libhdfs.
> "
> The interfaces in the attached patch attempt to address:
> A - Compression and decompression based on ByteBuffers (HDFS-2834)
> B - Zero-copy compression and decompression (HDFS-3051)
> C - Provide the caller a way to know how the max space required to hold
> compressed output.
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