F21 System Wide Change: lbzip2 as default bzip2 implementation

Mikolaj Izdebski mizdebsk at redhat.com
Wed Apr 2 22:37:36 UTC 2014

> This  clarification is significant.  The change proposal text needs to
> be updated to reflect this.

I will add a clarification tomorrow.

> As long as the encoding is guaranteed to be byte-for-byte identical to
> that produced by the original bzip2 (and libbz2) implementation, the
> risks are lowered.

No, encoding is almost never bytewise identical to bzip2, but it doesn't
have to be as long as the resulting bz2 file has correct format.

bzip2 itself changed encoding between versions without any impact on users.
Even the same version of bzip2 can produce different compressed files
for the same input with and with the same block size.

lbzip2 uses improved algorithms, which are not only faster, but allow for
slighty better compression ratio, for example:

$ echo test | bzip2 | wc -c
$ echo test | lbzip2 | wc -c

> Scenarios   affected  by  this  substitution  are  those  with  direct
> invocation of the command (from the command prompt, a shell script, or
> system() type call).

That's true.  And even in the unlikely case that something goes wrong,
developers (or even users themselves) have possibility to easily switch
back to bzip2.

Mikolaj Izdebski

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