yum-presto not on by default

[John Reiser]

On 09/23/2009 10:05 PM, Bill Nottingham wrote:
> So... just set the xz compression level to 2, let it be that way for future
> builds, and go about our business?

That's the best one-size-fits-all policy.  We can do better because the
current xz compression algorithm is at least as bad as O(n*n).  Restrict the
compression level to 2 for large .rpm, but use a higher level for smaller .rpm.
This will tend to avoid the largest time penalties yet still produce smaller
files for most .rpm.

Out of 4042 .rpm in my local cache (both i686 and x86_64):
    number    size
       60     >= 10MB
      138     >=  5MB
      235     >=  3MB
      344     >=  2MB
      635     >=  1MB
      720     >=   800KB
      921     >=   500KB
     1229     >=   300KB
     1503     >=   200KB
     2214     >=   100KB

Use something such as:
     ______size_____   level
     < 200KB             7 (current)
       200KB - 500KB     4
           >=  500KB     2

On top of that, there could be a sliding scale based on release date.
 From general availability release to next alpha, limit the level to 2
for all .rpm.  From alpha to beta, limit the level to 4.  From beta
to next general availability, use the size table.  This tends to avoid
large time penalties for the cases most likely to be seen by end users,
yet still tends to give better compression for a full release.

[Of course, fix the *STUPID* endianness property.]

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