From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Mon, 14 Jul 2008 12:25:54 GMT
Subject: Re: [PATCH 0/4] Honor core.deltaBaseCacheLimit during index-pack
Message-ID: <alpine.DEB.1.00.0807141322140.8950@racer>
In-Reply-To: <487B439F.8040902@op5.se>

Hi,

On Mon, 14 Jul 2008, Andreas Ericsson wrote:

> Sorry for being clueless here, but why does the older versions need
> to be kept in-memory anyway? Aren't we applying the delta each time
> we find one, repeatedly creating a new base-object in-memory for
> each delta? If we aren't doing that, why do we need more than just
> a small amount of memory just for keeping the delta?

Think of a delta chain of 49 delta objects, 1 base object.  Now 
reconstruct all of the objects.

If you do it one by one, not storing the intermediate results, you end up 
applying 1 delta for the first, 2 for the second (first the first, then 
the second), and so on, in total 1 + 2 + 3 + ... + 49 = 49 * 50 / 2 = 1225 
times.

Compare that to the 49 times when reusing the intermediate results.

Ciao,
Dscho