[lmi] ccache: little advantage to extra compression

[Greg Chicares]

Default ccache compression (a '0' argument causes the default to be used,
and the default is 1, so '--recompress 0' and '--recompress 1' have the
same result) already yields an "81.0% space savings", while recompressing
with an argument of '19' (the maximum that's guaranteed to be available)
gives an "85.5% space savings", at a cost of two and a half minutes with
three thousand percent of a CPU used. Even with 32 cores, that's two and
a half minutes that we'll probably never get back, as decompression speed
is nearly a constant function of compression level.

This outcome isn't startling, but the experiment seemed worth doing once.

/opt/lmi/src/lmi[0]$ccache --recompress 0 
Recompressing... 100.0% 
[===================================================================]

Original data:           6.8 GB
Old compressed data:   984.5 MB (14.5% of original size)
  - Compression ratio: 6.891 x  (85.5% space savings)
New compressed data:     1.3 GB (19.0% of original size)
  - Compression ratio: 5.264 x  (81.0% space savings)
Size change:          +304.2 MB
/opt/lmi/src/lmi[0]$time ccache --recompress 19
Recompressing... 100.0% 
[===================================================================]

Original data:           6.8 GB
Old compressed data:     1.3 GB (19.0% of original size)
  - Compression ratio: 5.264 x  (81.0% space savings)
New compressed data:   984.5 MB (14.5% of original size)
  - Compression ratio: 6.891 x  (85.5% space savings)
Size change:          -304.2 MB
ccache --recompress 19  4570.51s user 33.12s system 3040% cpu 2:31.41 total