Re: [PATCH 01/32] doc hash-file-transition: A map file for mapping between sha1 and sha256

> The v3 pack index file as documented has a lot of complexity making it
> difficult to implement correctly.  I worked with bryan's preliminary
> implementation and it took several passes to get the bugs out.
> 
> The complexity also requires multiple table look-ups to find all of
> the information that is needed to translate from one kind of oid to
> another.  Which can't be good for cache locality.
> 
> Even worse coming up with a new index file version requires making
> changes that have the potentialy to break anything that uses the index
> of a pack file.
> 
> Instead of continuing to deal with the chance of braking things
> besides the oid mapping functionality, the additional complexity in
> the file format, and worry if the performance would be reasonable I
> stripped down the problem to it's fundamental complexity and came up
> with a file format that is exactly about mapping one kind of oid to
> another, and only supports two kinds of oids.