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

From: Junio C Hamano <gitster@pobox.com>
Date: May 27, 2012, 09:27 UTC
Message-ID: <7vbolaotwj.fsf@alter.siamese.dyndns.org>
In-Reply-To: <20120527090407.GD86874@tgummerer>

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

Show 10 quoted lines

>> 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.