Re: If I were redoing git from scratch...

[Shawn Pearce <spearce@spearce.org>]

Linus Torvalds <torvalds@osdl.org> wrote:
> or for somebody who re-implements git in Java (where 
> performance isn't going to be the major issue anyway, and you probably do 
> "small" things like "commit" and "diff", and never do full-database things 
> like "git repack"), _then_ you can happily look at having something 
> fancier. Right now, it's too easy to just look at cumbersome interfaces, 
> and forget about the fact that those interfaces is sometimes what allows 
> us to practically do some things in the first place.

Yes and no.  :-)

As the only person here who has hacked on some of Git and also
reimplemented the core on disk data structures in Java I can say
I mostly agree with Linus.

Abstractions like the repository (to allow different GIT_DIRs to
be used in the same process) isn't really a big deal and is not
a large impact on performance.  They could be implemented in the
current C core.

But trying to abstractly represent an object in Java the same
way that it is represented in Git costs a huge amount of memory.
Java is at least 16 bytes of overhead per object, before you get to
store anything in it.  Translation: Linus is right, doing a real
implementation of "git repack" in Java is nuts.  It would barely
be able to handle git.git, let alone linux.git or mozilla.git.

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