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https://issues.apache.org/jira/browse/HADOOP-8148?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13401809#comment-13401809
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Todd Lipcon commented on HADOOP-8148:
-------------------------------------
bq. JNI is very problematic in several dimensions, but in terms of performance
take a look at https://issues.apache.org/jira/browse/HADOOP-6148
Sure, the pure Java approach was better than the crappy built-in JNI CRC. But
then we switched again back to JNI: HDFS-2080. With a _good_ implementation
based on direct buffers, it's way faster to go to C for most of this stuff,
since you can take advantage of SSE.
> 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, performance
> Reporter: Tim Broberg
> Assignee: Tim Broberg
> Attachments: hadoop8148.patch, zerocopyifc.tgz
>
>
> 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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