Re: [PATCH 0/4] Honor core.deltaBaseCacheLimit during index-pack

From: Shawn O. Pearce <spearce@spearce.org>
Date: Jul 14, 2008, 03:12 UTC
Message-ID: <20080714031242.GA14542@spearce.org>
In-Reply-To: <alpine.LFD.1.10.0807132220570.12484@xanadu.home>

Nicolas Pitre <nico@cam.org> wrote:

Show 13 quoted lines

> On Sun, 13 Jul 2008, Shawn O. Pearce wrote:
> 
> > This should resolve the obscene memory usage of index-pack when
> > resolving deltas for very large files.
> 
> I don't like this.  Not your patch, but rather the direction this whole 
> thing took in the first place, and now we have to bolt extra complexity 
> on top.
> 
> I have the feeling this is not the best approach, especially since many 
> long delta chains are going deep and all those intermediate objects are 
> simply useless once the _only_ delta child has been resolved and 
> therefore could be freed right away instead.

I thought about trying to free a base object if this is the last resolve_delta() call which would require that data, but I realized this is just a "tail-call optimization" and doesn't work in the more general case. This patch series is the best solution I could come up with to handle even the general case.

The only other alternative I can come up with is to change pack-objects (or at least its defaults) so we don't generate these massive delta chains. But there are already packs in the wild that use these chains, resulting in performance problems for clients.

-- 
Shawn.