[MERGE] Comparison cache to speed up diff

[John Arbash Meinel]

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Aaron Bentley wrote:

...

> 
>> If 'get_file()' is costing 50% of the total time to do 'bzr diff', do you have
>> any indications of why it is slow?
> 
> Knit indices.  Poor locality of reference.  Basically, we need a new
> repository format.
> 
>> It certainly seems like we can save a lot
>> more time by making that faster, than doing diff caching.
> 
> That's 50% of 3.556, or 1.8 seconds.  The diff caching saves about 1
> second.  This is not an either/or situation-- these gains are in the
> same order of magnitude, and are both worth having, imho.
> 
> Aaron

I thought your patch meant that we didn't have to extract the basis
text, since we already know the diff of the current file relative to its
basis revision. Or am I misunderstanding what you have done?

John
=:->
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