From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicolas Pitre <nico@cam.org>
Subject: Re: performance on repack
Date: Wed, 15 Aug 2007 15:00:14 -0400 (EDT)
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Cc: Martin Koegler <mkoegler@auto.tuwien.ac.at>,
	"Shawn O. Pearce" <spearce@spearce.org>,
	Git Mailing List <git@vger.kernel.org>
To: Jon Smirl <jonsmirl@gmail.com>
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On Wed, 15 Aug 2007, Jon Smirl wrote:

> On 8/15/07, Martin Koegler <mkoegler@auto.tuwien.ac.at> wrote:
> > git-pack-objects knows the order, in which it will use the objects.  A
> > seperate thread could pre-read the next object and wait until the main
> > thread starts processing it. After the read is complete, another
> > thread could start computing the delta index.
> 
> The hope is that the new adaptive read ahead code in the kernel will
> get this right and you won't need the second thread. Letting the
> kernel handle the read ahead will dynamically scale as other demands
> are made on the host. There's effectively only one read ahead cache in
> the system, only the kernel really knows how to divide it up between
> competing apps.

No read ahead will ever help the delta search phase.  Objects listed for 
deltification against each other are sorted in a way that results in 
reads from completely random location in the object store.

Normally the delta search phase is so compute intensive that the read 
shouldn't matter much.


Nicolas