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From "Stefan Bodewig (JIRA)" <>
Subject [jira] [Commented] (COMPRESS-333) bz2 stream decompressor is 10x slower than it could be
Date Fri, 05 Feb 2016 20:55:39 GMT


Stefan Bodewig commented on COMPRESS-333:

My memory has been failing me (it's been nine years), it has been creating corrupt output.

And even later it has been fixed and Ant (and thus Commons Compress) have started with using
a fork of the Hadoop code again.

> bz2 stream decompressor is 10x slower than it could be
> ------------------------------------------------------
>                 Key: COMPRESS-333
>                 URL:
>             Project: Commons Compress
>          Issue Type: Improvement
>            Reporter: Dawid Weiss
>             Fix For: 1.11
> This is related to COMPRESS-291. In short: decompressing 7z archives was an order of
magnitude slower in Java than with native tooling.
> My investigation showed that the problematic archive used bz2 streams inside. I then
did a quick hack-experiment which took bz2 decompressor from the Apache Hadoop project (the
Java version, not the native one) and replaced the default one used for bz2 stream decompression
of the 7z archiver in commons.
> I then ran a quick benchmark on this file:
> {code}
> {code}
> The decompression speeds are (SSD, the file was essentially fully cached in memory, so
everything is CPU bound):
> {code}
> native {{7za}}: 13 seconds
> Commons (original): 222 seconds
> Commons (patched w/Hadoop bz2): 30 seconds
> Commons (patched w/BufferedInputStream): 28 seconds
> {code}
> Yes, it's still 3 times slower than native code, but it's no longer glacially slow...

> My patch is a quick and dirty proof of concept (not committable, see [1]), but it passes
the tests. Some notes:
> - Hadoop's stream isn't suited for handling concatenated bz2 streams, it'd have to be
either patched in the code or (better) decorated at a level above the low-level decoder,
> - I only substituted the decompressor in 7z, but obviously this could benefit in other
places (zip, etc.); essentially, I'd remove BZip2CompressorInputStream entirely.
> - while I toyed around with the above idea I noticed a really annoying thing -- all streams
are required to extend {{CompressorInputStream}}, which only adds one method to count the
number of consumed bytes. This complicates the code and makes plugging in other implementations
of InputStreams more cumbersome. I could get rid of CompressorInputStream entirely with a
few minor changes to the code, but obviously this would be backward incompatible (see [2]).
> References:
> [1] GitHub fork, {{bzip2}} branch:
> [2] Removal and cleanup of CompressorInputStream:

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