On Wed, Apr 15, 2009 at 07:30:32PM +0200, Robin Rosenberg wrote:
> Take a look at ccache. It doesn't use Git, but it uses hashes of source, and
> compiler flags and associates that with the resulting object files, so it
> can avoid compiling. If you are building largs C/C++ (especially C++)
> projects you want it.
In theory, one could improve something like ccache by asking git the
sha-1 of the file. Since git maintains a cache based on stat info, you
can get away with not looking at the file contents at all (which saves
CPU time in hashing, but also helps a lot when building from a cold
cache).
In practice, this doesn't help because:
1. ccache looks at more than just the file itself. I believe it
actually runs it through cpp and hashes that.
2. People combine ccache with make; if the stat data hasn't changed,
in most cases, you will skip building before you even get to
ccache.
But one could probably design a system to replace both ccache and make
that relies on git's fast sha-1 reporting to avoid duplicate work. I
suspect nobody has bothered because make+ccache is "fast enough" that
the added complexity would not be worth it.
-Peff
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