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

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Hi,

On Mon, 14 Jul 2008, Shawn O. Pearce wrote:

> Nicolas Pitre <nico@xxxxxxx> wrote:
> > 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.

However, for cases like Stephan's I assume this is the rule.  If you 
think of it, most use cases for such a big blob are one-user, 
append-only.

> 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.

But the long chains make the pack actually as efficient as it is...

Ciao,
Dscho

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