Re: Git performance results on a large repository

From: Nguyen Thai Ngoc Duy <pclouds@gmail.com>
Date: Feb 5, 2012, 03:47 UTC
Message-ID: <CACsJy8Bf95JMp1qOiruR7+Tdi7JN42KNeMqGLud+z3O26DREnw@mail.gmail.com>
In-Reply-To: <243C23AF01622E49BEA3F28617DBF0AD5912CA85@SC-MBX02-5.TheFacebook.com>

On Sun, Feb 5, 2012 at 1:05 AM, Joshua Redstone <joshua.redstone@fb.com> wrote:

> It's also conceivable that, if there were an external interface in git to attach other
> systems to efficiently report which files have changed (e.g., via file-system integration),
> it's possible that we could omit managing the index in many cases.
> I know that would be a big change, but the benefits are intriguing.

The "interface to report which files have changed" is exactly "git update-index --[no-]assume-unchanged" is for. Have a look at the man page. Basically you can mark every file "unchanged" in the beginning and git won't bother lstat() them. What files you change, you have to explicitly run "git update-index --no-assume-unchanged" to tell git.

Someone on HN suggested making assume-unchanged files read-only to avoid 90% accidentally changing a file without telling git. When assume-unchanged bit is cleared, the file is made read-write again.

-- 
Duy