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From "Stefan Bodewig (JIRA)" <>
Subject [jira] [Commented] (COMPRESS-388) Improve concurrent reads from ZipFile
Date Tue, 25 Apr 2017 08:46:04 GMT


Stefan Bodewig commented on COMPRESS-388:

[~kvr] I see where you are heading and agree it should be a separate proposal. As for moving
stuff from {{ZipFile.Entry}} one thing to consider is that it may only be useful for entries
read from a {{ZipFile}} while {{ZipEntry}} is also used by people creating archives or reading
them via {{ZipArchiveInputStream}}. Just a thought.

I'll look into the PR for this issue in detail tonight (UTC+2, that is).

> Improve concurrent reads from ZipFile
> -------------------------------------
>                 Key: COMPRESS-388
>                 URL:
>             Project: Commons Compress
>          Issue Type: Improvement
>          Components: Archivers
>    Affects Versions: 1.13
>         Environment: Any
>            Reporter: Zbynek Vyskovsky
>              Labels: patch, performance
>             Fix For: 1.14
>   Original Estimate: 2h
>  Remaining Estimate: 2h
> Concurrent reads on the ZipFile archive is terribly slow on multiprocessor systems. On
my 4 CPU laptop it shows 26 reads/s vs 2 reads/s on 100MB samples for example.
> The cause is the use of synchronized blocks to access the underlying file channel. This
may be required for generic SeekableByteChannel but most commonly there is FileChannel implementation
which supports lock-free reading from any position (i.e. using pread/pwrite system calls or
their equivalent).
> With the fix the performance is about 10 times faster (on 4 CPU system, with more processor
the difference should grow significantly).

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