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[Bug-tar] [Fwd: Bug#543913: "tar tf" uses read() instead of lseek(), ma

From: Bdale Garbee
Subject: [Bug-tar] [Fwd: Bug#543913: "tar tf" uses read() instead of lseek(), making it slow]
Date: Thu, 27 Aug 2009 09:07:29 -0600

A user of our Debian packages of tar points out that it might be more
efficient to use lseek() in some circumstances, particularly for
archives containing a small number of large files.


--- Begin Message --- Subject: Bug#543913: "tar tf" uses read() instead of lseek(), making it slow Date: Thu, 27 Aug 2009 14:09:35 +0200
Package: tar
Version: 1.20-1
Severity: normal

When running "tar tf" on a large tarball containing few large files, tar
becomes incredibly slow. The reason for this is that tar issues many
read()s to skip the file content, but as it doesn't need the content, it
throws it away. GNU tar could just use lseek() like libarchive and busybox

Also a problem is extracting only one file from said tarball, where the
other files do not need to be read for just that one to be extracted.

The problem exists on all versions of GNU tar and was confirmed to exist
on at least all versions starting from etchthe one shipped with Etch.

-- System Information:
Debian Release: 5.0.2
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.26-2-amd64 (SMP w/1 CPU core)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages tar depends on:
ii  libc6                         2.9-12     GNU C Library: Shared libraries

tar recommends no packages.

Versions of packages tar suggests:
ii  bzip2                         1.0.5-2    high-quality block-sorting file co
pn  ncompress                     <none>     (no description available)

-- no debconf information

--- End Message ---

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