Re: [GSoC] Designing a faster index format

From: Thomas Rast <trast@student.ethz.ch>
Date: Mar 21, 2012, 12:51 UTC
Message-ID: <871uomrubl.fsf@thomas.inf.ethz.ch>
In-Reply-To: <CACsJy8D2RwG-Nr5btcQj0f9=JACvH6mf7LNi=Jnb_y+j4_2u0A@mail.gmail.com>

Nguyen Thai Ngoc Duy <pclouds@gmail.com> writes:

Show 15 quoted lines

> On Wed, Mar 21, 2012 at 4:22 PM, Thomas Gummerer <t.gummerer@gmail.com> wrote:
>>
>> On Mar 21, 2012, at 2:29 AM, Nguyen Thai Ngoc Duy wrote:
>>
>> 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.

Note that switching the checksum used already requires a backwards-incompatible change of the index format. If we are going to do that, I'm somewhat opposed to not also revising it along the lines sketched by Shawn (at least).

See my reply to Elton Sky

  http://thread.gmane.org/gmane.comp.version-control.git/193550/focus=193571

for links to some threads you may want to look at.

-- 
Thomas Rast
trast@{inf,student}.ethz.ch