Re: [PATCH v5 8/8] sha1_file: refactor has_sha1_file_with_flags

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Jonathan,

On Tue, 18 Jul 2017, Jonathan Tan wrote:

> On Tue, 18 Jul 2017 12:30:46 +0200
> Christian Couder <christian.couder@gmail.com> wrote:
> 
> > On Thu, Jun 22, 2017 at 2:40 AM, Jonathan Tan <jonathantanmy@google.com> wrote:
> > 
> > > diff --git a/sha1_file.c b/sha1_file.c
> > > index bf6b64ec8..778f01d92 100644
> > > --- a/sha1_file.c
> > > +++ b/sha1_file.c
> > > @@ -3494,18 +3494,10 @@ int has_sha1_pack(const unsigned char *sha1)
> > >
> > >  int has_sha1_file_with_flags(const unsigned char *sha1, int flags)
> > >  {
> > > -       struct pack_entry e;
> > > -
> > >         if (!startup_info->have_repository)
> > >                 return 0;
> > > -       if (find_pack_entry(sha1, &e))
> > > -               return 1;
> > > -       if (has_loose_object(sha1))
> > > -               return 1;
> > > -       if (flags & HAS_SHA1_QUICK)
> > > -               return 0;
> > > -       reprepare_packed_git();
> > > -       return find_pack_entry(sha1, &e);
> > > +       return sha1_object_info_extended(sha1, NULL,
> > > +                                        flags | OBJECT_INFO_SKIP_CACHED) >= 0;
> > >  }
> > 
> > I am not sure if it could affect performance (in one way or another) a
> > lot or not but I just wanted to note that has_loose_object() calls
> > check_and_freshen() which calls access() on loose object files, while
> > sha1_object_info_extended() calls sha1_loose_object_info() which calls
> > stat_sha1_file() which calls lstat() on loose object files.
> > 
> > So depending on the relative performance of access() and lstat() there
> > could be a performance impact on repos that have a lot of loose object
> > files.
> 
> That is true, but from what little I have read online, they have about
> the same performance.

Then your online sources missed out on what we have in compat/mingw.[ch].
I would expect _waccess() (which is used to emulate access()) to be
substantially faster than the hoops we jump through to emulate lstat().

Ciao,
Dscho