Making diff fast (was Re: Some notes on distributed SCM)

[Aaron Bentley]

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Daniel Phillips wrote:
> On Sunday 10 April 2005 18:17, Aaron Bentley wrote:

>>This is what Arch does, and it's quite slow on large trees.  Robert
>>Collins has recently improved this in Baz, but it doesn't change the
>>fact that it's an O(versioned files) operation, rather than O(changed
>>files).
> 
> 
> But statting the full working copy kernel tree takes less than .1 second if 
> the dentries are in cache, and it takes less than 5 seconds to get them in 
> cache.  What is wrong with that?

5 seconds isn't fast enough.  There's a huge psychological difference
between 5-second and subsecond response times.  At 5 seconds, it's still
an awkward delay.  If you just want a reminder of what you changed, it's
annoying.

If we can find ways to make operations O(changed files), then we avoid
penalizing people with large projects.

If subsecond is the common case, that's great.  Otherwise, I really do
believe there's room for improvement.

Aaron
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