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https://issues.apache.org/jira/browse/HADOOP-7657?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13118022#comment-13118022
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Yann Collet commented on HADOOP-7657:
-------------------------------------
Hi
I'm the author of LZ4.
Since it is mentionned in this issue, i feel compelled to provide some more
information.
There are in fact two container modes created for LZ4, but i only cared
publishing the first one (stream mode), since there was very little interest
expressed in the second one (seekable mode).
The seekable mode has these properties :
- Selectable block size (as a power of 2, from 512 bytes to 16 MB; extension
reserved up to 1GB)
- Handle uncompressed blocks
- Blocks can be forced to start at aligned positions (2 bytes, 4 bytes, 8
bytes, etc.)
- Compressed file starts with an array which provides the start position of
each block
- Array value can be stored as direct position or block size (the second
solution can reduce the size of array)
- Automatic sizing of array values (16, 32 or 64 bits).
- File size limited to 256 TB
Since the array must be written at the beginning of the compressed file, it is
not compatible with "pipe mode".
The only use-case for seekable mode so far has been compressed ISO. So i've not
spent much time on it.
I'm a bit surprised it would be usefull for Hadoop since i expect Handle to
handle its own container format, and a probably much adapted one.
Anyway, since r35 is out, i would advise to use something like 64KB blocks.
This way, each block is independant, and can be
fetched/stored/duplicated/decoded independantly, in its own thread, CPU,
machine or cluster.
Hope this helps
Regards
> Add support for LZ4 compression
> -------------------------------
>
> Key: HADOOP-7657
> URL: https://issues.apache.org/jira/browse/HADOOP-7657
> Project: Hadoop Common
> Issue Type: Improvement
> Reporter: Mr Bsd
> Labels: compression
>
> According to several benchmark sites, LZ4 seems to overtake other fast
> compression algorithms, especially in the decompression speed area. The
> interface is also trivial to integrate
> (http://code.google.com/p/lz4/source/browse/trunk/lz4.h) and there is no
> license issue.
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