Re: [PATCH 4/6] introduce a commit metapack

From: Jeff King <peff@peff.net>
Date: Jan 29, 2013, 11:13 UTC
Message-ID: <20130129111322.GB11055@sigill.intra.peff.net>
In-Reply-To: <5107A36D.2050307@alum.mit.edu>

On Tue, Jan 29, 2013 at 11:24:45AM +0100, Michael Haggerty wrote:

Show 14 quoted lines

> On 01/29/2013 10:16 AM, Jeff King wrote:
> > When we are doing a commit traversal that does not need to
> > look at the commit messages themselves (e.g., rev-list,
> > merge-base, etc), we spend a lot of time accessing,
> > decompressing, and parsing the commit objects just to find
> > the parent and timestamp information. We can make a
> > space-time tradeoff by caching that information on disk in a
> > compact, uncompressed format.
> > 
> > TODO: document on-disk format in Documentation/technical
> > TODO: document API
> 
> Would this be a good place to add the commit generation number that is
> so enthusiastically discussed on the mailing list from time to time?

Yes, that is one of my goals. We may even be able to just replace the timestamp field in the cache with a generation number. When it gets pretty-printed we pull it out of the commit message again anyway, so in theory the only use inside "struct commit" is for ordering. But I haven't looked at all of the use sites yet to be sure nobody is depending on it being an actual date stamp.

-Peff