Re: [RFC] Cache negative delta pairs

From: Jeff King <peff@peff.net>
Date: Jun 29, 2006, 18:07 UTC
Message-ID: <20060629180719.GB4392@coredump.intra.peff.net>
In-Reply-To: <Pine.LNX.4.64.0606291154510.1213@localhost.localdomain>

On Thu, Jun 29, 2006 at 12:39:31PM -0400, Nicolas Pitre wrote:

> You do that lookup for every delta match attempt.  Instead it could be 
> done once for the whole window attempt, potentially reducing the cache 
> size by a factor of 20, and it might be faster too.

I'm not convinced this will provide good cache hit characteristics, and I'm not convinced it's semantically correct (see my other mail).

> You could simply recreate the cache on each run.  Or just keep a bitmap

Yes, that would probably work and would be quite easy to do with the existing code.

Show 6 quoted lines

> First, I think it should be ignored (but still created) when 
> --no-reuse-delta is passed.  Then, it should not be created (but still 
> looked up if it exists and --no-reuse-delta is not provided) when the 
> pack index file is also not created.  I don't think it is worth making 
> this further configurable, and given the suggested strategy above the 
> cache should remain fairly small.

Those suggestions make sense to me.

-Peff