Re: [PATCH 01/02/RFC] implement a stat cache

From: Johan Herland <johan@herland.net>
Date: Apr 21, 2008, 08:41 UTC
Message-ID: <200804211041.41760.johan@herland.net>
In-Reply-To: <20080421005340.GA2631@dpotapov.dyndns.org>

On Monday 21 April 2008, Dmitry Potapov wrote:

Show 9 quoted lines

> On Sun, Apr 20, 2008 at 04:07:35PM -0700, Linus Torvalds wrote:
> > Junio, what was the logic for that whole "has_symlink_leading_path()"
> > thing? I forget. Whatever, it's broken.
> 
> ===
> commit f859c846e90b385c7ef873df22403529208ade50
> Author: Junio C Hamano <junkio@cox.net>
> Date:   Fri May 11 22:11:07 2007 -0700
>

[snip snip]

Show 13 quoted lines

> ===
> 
> And there are some cases where stat() on path is desirable:
> http://www.spinics.net/lists/git/msg63988.html
> 
> So while stat information for regular files is cached in the index,
> stat information for directories is not cached, and that appears to
> be wrong. Maybe, Lucano's cache makes sense if it stores only stat
> information for directories.
> 
> IIRC, some time ago, an otherwise reasonable patch for .gitignore was
> rejected just because it would drive the number calls to lstat() up as
> these calls on directories are not cached in the index.

Pardon me for butting in (and I'm honestly NOT trying to start a flamewar), but I'm wondering if this could be solved by tracking directories in the index. AFAICS it would:

- Help bring the number of lstat() calls down (since we can cache the
  lstat() results for directories like we currently do for regular files)

- More easily detect complicated cases like "add across symlinks" (see
  Junio's email at the spinics.net link above)

- (less important) When discussing empty directory support several months
  ago, ISTR one of the biggest hurdles being that directories were not
  tracked in the index

I don't know much about how the index is implemented (few do, I think), so if there is a glaringly obvious reason why tracking directories in the index is a bad idea, please enlighten me.

...Johan

-- 
Johan Herland, <johan@herland.net>
www.herland.net