Re: [PATCH 3/6] Stop producing index version 2

> 2012/2/5 Junio C Hamano <gitster@pobox.com>:
>> Nguyễn Thái Ngọc Duy  <pclouds@gmail.com> writes:
>>
>>> read-cache.c learned to produce version 2 or 3 depending on whether
>>> extended cache entries exist in 06aaaa0 (Extend index to save more flags
>>> - 2008-10-01), first released in 1.6.1. The purpose is to keep
>>> compatibility with older git. It's been more than three years since
>>> then and git has reached 1.7.9. Drop support for older git.
>>
>> Cc'ing this, as I suspect this would surely raise eyebrows of some people
>> who wanted to get rid of the version 3 format.
>
> Version 3 was a mistake because of the variable length record sizes.
> Saving 2 bytes on some records that don't use the extended flags makes
> the index file *MUCH* harder to parse. So much so that we should take
> version 3 and kill it, not encourage it as the default!

> <thinking type="wishful" probability="never-happen"
> probably-inflating-flame-from="linus">
>
> I have long wanted to scrap the current index format. I unfortunately
> don't have the time to do it myself. But I suspect there may be a lot
> of gains by making the index format match the canonical tree format
> better by keeping the tree structure within a single file stream,
> nesting entries below their parent directory, and keeping tree SHA-1
> data along with the directory entry. For one thing the index would be
> able to register an empty subdirectory, rather than ignoring them. It
> would also better line up with the filesystem's readdir() handling,
> giving us more sane logic to compare what readdir() tells us exists
> against what the index thinks should be in the same file. And the
> overall index should be smaller, because we don't have to repeat the
> same path/to/a/file/for/every/file/in/that/same/directory/tree.
> Reconstructing the path strings at read time into a flat list should
> be pretty trivial, and still keep the parallel lstat calls running off
> a flat list working well for fast status operations.
>
> </thinking>