[Gnu-arch-users] Re: [PATCH] arch speedups on big trees

[Miles Bader]

On Thu, Jan 08, 2004 at 09:27:38AM -0500, Chris Mason wrote:
> So as soon as the diff program makes output, we open the tmp file?
> 
> Because of arch_binary_files_differ(), we are 100% sure diff is going to
> have output.  So just open the tmp file to start with and make life easy

I don't know -- the current codebase doesn't seem to use
arch_binary_files_differ before diffing; maybe your code-base does (but
honestly, I'm really hoping Tom _doesn't_ merge your branch, because there
are currently way, way, too many problems with it).

Doing a binary comparison before diffing is a solution to this problem,
but of course ends up reading the files twice.  This sort of thing is
_normally_ covered up in NFS (and in linux, in local filesystems too) by
short-term caching, _but_ I'm not really sure how confident I can be about
this; for instance, what if there are lots of really big files, will only
parts of them be cached, resulting in redundant reads even when very close
in time?  Does the added efficiency of not invoking the diff program make
it worthwhile anyway?  I guess the answer probably depends on what
filesystem you're using...

-Miles
-- 
`There are more things in heaven and earth, Horatio,
 Than are dreamt of in your philosophy.'