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https://issues.apache.org/jira/browse/COMPRESS-438?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stefan Bodewig resolved COMPRESS-438.
-------------------------------------
Resolution: Fixed
Fix Version/s: 1.16
added a BufferedInputStream unconditionally in ZipFile.
> ZipFile should create a buffered input stream for decoders inside
> getInputStream(ZipArchiveEntry)
> -------------------------------------------------------------------------------------------------
>
> Key: COMPRESS-438
> URL: https://issues.apache.org/jira/browse/COMPRESS-438
> Project: Commons Compress
> Issue Type: Improvement
> Reporter: Dawid Weiss
> Priority: Minor
> Fix For: 1.16
>
> Attachments: Check.java
>
>
> When decoders read from a raw underlying stream (such as a file channel), the
> performance can degrade an order of magnitude compared to the case when
> there's a simple buffer in between the physical data source and the codec.
> See COMPRESS-380 for an example of this.
> The API of {{ZipFile}} is straightforward and tempting enough that blocks of
> code such as:
> {code}
> try (ZipFile zfile = new ZipFile("/path/to/zip.zip")) {
> Enumeration<ZipArchiveEntry> entries = zfile.getEntries();
> while (entries.hasMoreElements()) {
> ZipArchiveEntry e = entries.nextElement();
> try (InputStream is = zfile.getInputStream(e)) {
> // do something with is
> }
> }
> }
> {code}
> seem perfectly justified. The above code suffers from severe performance
> degradation compared to prebuffered input. Severe means *severe*. Here are
> some stats from running a snippet of code similar to the above to "just
> decompress" the same input (~80mb) compressed with different methods.
> {code}
> # Input compressed with 7za.
> 7za a -mm=deflate archive-deflate.zip input
> 7za a -mm=deflate64 archive-deflate64.zip input
> 7za a -mm=bzip2 archive-bzip2.zip input
> {code}
> Current master branch:
> {code}
> # Direct BoundedInputStream
> archive-deflate.zip 0.39 sec., 37,893,785 archived => 81,502,941 decompressed
> archive-deflate64.zip 26.98 sec., 37,856,848 archived => 81,502,941
> decompressed
> archive-bzip2.zip 49.16 sec., 38,166,089 archived => 81,502,941 decompressed
> {code}
> And a simple patch wrapping BoundedInputStream with a BufferedInputStream
> (deflate64 and bzip2 only, deflate uses java's internal inflater and it
> prebuffers stuff internally).
> {code}
> # wrapped with BufferedInputStream, bufferSize = 512
> archive-deflate.zip 0.38 sec., 37,893,785 archived => 81,502,941 decompressed
> archive-deflate64.zip 0.95 sec., 37,856,848 archived => 81,504,783
> decompressed
> archive-bzip2.zip 3.00 sec., 38,166,089 archived => 81,502,941 decompressed
> # wrapped with BufferedInputStream, bufferSize = 1024
> archive-deflate.zip 0.41 sec., 37,893,785 archived => 81,502,941 decompressed
> archive-deflate64.zip 0.97 sec., 37,856,848 archived => 81,504,783
> decompressed
> archive-bzip2.zip 2.95 sec., 38,166,089 archived => 81,502,941 decompressed
> # wrapped with BufferedInputStream, bufferSize = 4096
> archive-deflate.zip 0.42 sec., 37,893,785 archived => 81,502,941 decompressed
> archive-deflate64.zip 0.89 sec., 37,856,848 archived => 81,504,783
> decompressed
> archive-bzip2.zip 2.97 sec., 38,166,089 archived => 81,502,941 decompressed
> {code}
> The difference should be evident, even with a tiny buffer of 512 bytes. To
> put this into perspective on a larger archive:
> {code}
> archive-deflate.zip 7.68 sec., 1,235,209,977 archived => 1,339,916,520
> decompressed
> archive-deflate64.zip 784.87 sec., 1,233,470,780 archived => 1,339,916,520
> decompressed
> {code}
> deflate64 improves by ~4900%...
> {code}
> archive-deflate.zip 8.12 sec., 1,235,209,977 archived => 1,339,916,520
> decompressed
> archive-deflate64.zip 16.24 sec., 1,233,470,780 archived => 1,339,981,595
> decompressed
> {code}
> I also see that {{ExplodingInputStream}} is already wrapping {{bis}} in a
> buffered input stream, so I don't see any reason why this shouldn't be done
> for other compressor streams. An even better patch (to me) would be to modify
> the constructors of {{Deflate64CompressorInputStream}} and
> {{BZip2CompressorInputStream}} and add a boolean parameter {{unbuffered}}:
> then people would know what they're doing when they pass some input stream
> and {{true}} to such a constructor. The default, single-argument constructor
> would simply delegate to {{constructor(inputStream, false)}} to ensure an
> input buffer in between the decoder and the raw stream.
> The patch is trivial, so I don't attach it?
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