Re: [PATCH] grep: do not do external grep on skip-worktree entries

From: Jeff King <peff@peff.net>
Date: Jan 4, 2010, 07:26 UTC
Message-ID: <20100104072659.GA10611@coredump.intra.peff.net>
In-Reply-To: <7vhbr2pcsh.fsf@alter.siamese.dyndns.org>

On Sun, Jan 03, 2010 at 11:08:46PM -0800, Junio C Hamano wrote:

Show 6 quoted lines

> > I have to wonder, though...did anybody ever actually profile our
> > internal grep to find out _why_ it was so much slower than GNU grep?
> 
> I vaguely recall that somebody fairly competent mentioned that modern grep
> implementations are based on DFA engines, but I offhand don't remember if
> the discussion had concrete numbers.

Probably this:

  http://article.gmane.org/gmane.comp.version-control.git/41685

Also of interest is:

  http://article.gmane.org/gmane.comp.version-control.git/50174

The pcre analysis there came from just using the "pcreposix" header, I think. From my limited research, modern pcre may have some tuning options (including a DFA engine!) that could do a lot better.

-Peff