Re: [GSoC] Designing a faster index format

From: Nguyen Thai Ngoc Duy <pclouds@gmail.com>
Date: Mar 21, 2012, 11:18 UTC
Message-ID: <CACsJy8Aga7OYfAL0X+SyHxaF4gzGs+cvqfX+DZNXCua8c9XMig@mail.gmail.com>
In-Reply-To: <CALgYhfPOJpKbM__iU4KvChWeXWyyhWb2ocR-SLvrQQHNw5F5dQ@mail.gmail.com>

On Wed, Mar 21, 2012 at 6:08 PM, Thomas Gummerer <t.gummerer@gmail.com> wrote:

Show 17 quoted lines

>> > However I got one more question, since I'm not yet really familiar with
>> > the
>> > code and internal structure of git, what exactly does the SHA1 over the
>> > index exactly achieve? Is it only for checking if the index is still
>> > correct
>> > for the next time it is used and has not been changed or is there a more
>> > important function of it?
>>
>> It makes sure the index is not corrupt (by disk faults for example). I
>> don't think it is used for anything else. Cheaper checksum can be used
>> if good enough for the index. See
>> http://thread.gmane.org/gmane.comp.version-control.git/190016 and the
>> following reply.
>
> Ok thanks. I guess that could be another way to speed things up, but for
> really big repositories probably it won't be enough and the reduction of the
> complexity as described in the proposal is the way to go.

Yeah. A good format should not require checksuming the whole index, if we only need to read/verify a few entries, I think.

> Is the current complexity O(n)?

I think so. Have a look at read-cache.c, read_index_from for reading and write_index for writing, as a starting point.

-- 
Duy