[Libreoffice] ccache support

[Terrence Enger]

On Fri, 2011-09-09 at 20:22 +0200, Lubos Lunak wrote:
> On Friday 09 of September 2011, Norbert Thiebaud wrote:
> 
>  Could somebody else, preferably with a somewhat more common system :), post 
> their results, so that we can compare? I assume the ccache overhead (caused 
> by I/O I'd say) is exceptionally high here, but I still doubt ccache warrants 
> being enabled by default just like that.
> 
> > I don't do that in configure for the same reason we don't change
> > CCACHE_DIR or the cache dir size.
> > Using ccache if available is one thing... but trying to
> > 'auto-magically' optimize ccache is another can of worms altogether...
> 
>  I think the case above shows that there are some worms even in the one thing.
> 
> 

Well, let me throw some more numbers on the pile, about
space, number of cached files, and hits.  Short version:
cache compression reduces cache size by very roughly a
factor of 5.

My RAM is so small, at 512MB, that I omit timings; besides I
kept using the system for other things at the same time.
All compiles yesterday were with cache compression turned on.

"Size" is in KB as reported by `du --summarize ~/.ccache`.
Files, hits, and misses are from `ccache -s`.

I started yesterday with a cache holding files from a number
of previous builds of LibreOffice, some of them compressed,
but lots not (just because I keep forgetting to set
CCACHE_COMPRESS; yes, I have now added that to my .bashrc):
    size   : 9563228
    files  : 79453
    hits   : 54662 + 510
    misses : 39198
I calculate average file size 120.02KB

After some unsuccessful attempts to rebuild:
    size   : 9618256
    files  : 81585
    hits   : 54874 + 629
    misses : 39990
I calculate average file size 117.85KB and average size
21.03KB for the 2184 new files.

After successful complete build, which cleaned out part of
the cache:
    size   : 9123940
    files  : 99112
    hits   : 62377 + 3080
    misses : 48614
I calculate average file size 92.06KB.

FWIW, and HTH
Terry.