[Monotone-devel] Re: linus talk on git

[Graydon Hoare]

Nuno Lucas wrote:

> > Maybe I got this wrong, but based on what I have seen so far of this
> > talk, I couldn't help but think that Linus didn't consult the Monotone
> > developers with his concerns about speed, why it was slow, or how much
> > work it would take to improve its speed.

He talked to us a bit. There were a variety of issues.

Some "style" issues: I wrote monotone for flexibility, debug-ability, 
cryptographic integrity, experimentation. We've rearranged and replaced 
subsystems several times over (field-upgrading our databases as we went) 
as we were learning. This is important to me, but it imposed a major set 
of across-the-board speed penalties: notably that the disk format, 
network format and memory formats are all different, and none is 
optimized at all for constant factors. Lots of transformation and 
re-verification. Git is written in "performance above all else" style, 
but it's much more rigid in its shared data structure and much less 
forgiving about having its midsection field-upgraded. There's also the 
overhead of my quirky C++ style vs. kernel-hacker C style. I don't like 
my code twiddling pointers a lot. I like a lot of automatic assertions. 
Git style feels to me like asking for memory faults. Maybe I'm a bit of 
a wuss.

Some "design" issues: monotone was more like git early on (and it was 
actually way faster than the post-changeset code) but we abandoned that 
structure because we wanted to model long-term file and directory 
identities, because users claim they exist and claim to care about them. 
Linus rejected this notion. We didn't really want to go back on that 
decision: it matters a lot to Java developers. C developers don't care 
as much since they never rename files.

Some "bad timing" issues: I was on vacation and we had *just* landed 
some profoundly slow changes. He got us at our slowest moment. And he's 
a sort of impatient guy to begin with.

The last point made the worst first impression. The first two probably 
doomed us to be undesirable to Linus, even if we'd made a good first 
impression. But it's all water under the bridge now anyways.

-graydon