[PACKS] Performance opportunities.

[Ian Clatworthy]

John Arbash Meinel wrote:
> Robert Collins wrote:

>> Secondly we sha the working tree twice on an initial commit (bzr init;
>> bzr add; bzr commit) because everything is a miss - thats only
>> ~3seconds, but 3 seconds on a 263 is still > 1%.
> 
> 
> It may be a bit more than that, because we are reading the file 2 times. Which
> could certainly mess up the caching algorithms. (We read the file 1 time when
> building up the inventory, and then a second time when we go to commit the texts.) 

My "quicker initial commit" patch fixes this problem for the initial
commit of a file.

> (In my mind, we might allow for _iter_changes to have 3 possibilities,
> definitely changed, definitely not changed, and 'maybe changed'.)

Rob has a commit_candidates branch that has a cool new commit-friendly
iterator. I'm in the process of integrating it into one of my branches.
Before I can use it though, I need to get the "inventory delta support
for CommitBuilder" patch completed. That's up for review now.

Ian C.