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

[Nguyen Thai Ngoc Duy <pclouds@gmail.com>]

On Sun, May 27, 2012 at 4:27 PM, Junio C Hamano <gitster@pobox.com> wrote:
> 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".

Or harder things like "ls-files -- 't/*.sh'"

> 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.

and "ls-files -uc" can show how you combine unmerged entries back.
There's also entry existence check deep in "ls-files -o" that you can
show how good bsearch on trees is, though that might be going too far
for an experiment because the call chain is really deep, way outside
ls-files.c:

show_files (builtin/ls-files.c)
 fill_directory (dir.c)
  read_directory
   read_directory_recursive
    treat_path
     treat_one_path
      treat_directory
       directory_exists_in_index
        cache_pos_name (read-cache.c)

I just want to make sure that by exercising the new format with some
real problems, we are certain we don't overlook anything in designing
the format (or else could be fixed before finalizing it).
-- 
Duy