Diffing commits of big files is slow

[Daniel Clemente]

In a pack-0.92 branch with latest Bazaar (1.17dev), I replaced a 40 Mb video with a newer version (30Mb). 

  I am intrigued as to why the following operations are so slow:

- at the GTK interface (bzr vis), click on that particular revision to see the diff. An strace revealed that Bzr was comparing lots of binary data

- bzr diff -r 40: it stops some seconds until it can say: === modified file 'videos/Patata.ogg'. Binary files videos/Patata.ogg	2009-06-18 21:29:07 +0000 and videos/Patata.ogg	2009-06-21 22:45:25 +0000 differ

  The two videos are clearly different right in the headers, so testing for inequality could be instant. What else does Bazaar do and why is this favorable to the user?

  Format 2a has also this non-instant diff.


-- Daniel