Re: [GSoC] Designing a faster index format - Progress report

[Junio C Hamano <gitster@pobox.com>]

Thomas Gummerer <t.gummerer@gmail.com> writes:

>> No, read_index_from would go through the normal tree->list conversion.
>> What I'd like to see is what it looks like when a command accesses
>> index v5 directly in tree form, taking all advantages that tree-form
>> provides, and how we should deal with old index versions while still
>> supporting index v5 (without losing tree advantages)
>
> Ah ok, thanks for the clarification, I understand what you meant now.
> I think however, that it's not very beneficial to do this conversion
> now. git ls-files needs the whole index file anyway, so it's probably
> not a very good test.

Think about "git ls-files t/" and "git ls-files -u".  

The former obviously does *not* have to look at the whole thing, even
though the current code assumes the in-core data structure that has the
whole thing in a flat array.  IIRC, you had unmerged entries tucked at the
end outside the main index data, so the latter is also an interesting
demonstration of how wonderful the new data format could be.

Unlike other commands like status and diff that may need to look at things
other than the index, the core functionalitly of ls-files is purely about
the index.  I do not understand why you think it is not a good test case.
If an updated index structure cannot even improve ls-files, there is no
hope it can improve other more complex commands that need to walk the
index and something else in parallel.