We just wrapped up RailsConf 2008. A lot has been said about RailsConf elsewhere, so
as the program chair I’ll just say “thank you” to the speakers, attendees, co-organizers, sponsors, and
everyone else for making it the best conference I’ve ever been to.
A lot of exciting things happened. Among the most exciting to me was the public unveiling of
Maglev. I’ve had a version of Maglev on my computer for about a month now, but
I haven’t been able to talk about it. Now that it has been announced, most things I know are fair game.
Avi Bryant and I met at the first RubyConf. He’s been a fan and friend of Ruby ever
since. He happens to be doing mostly Smalltalk these days, but he’s been following the Ruby and (more
recently) Rails communities closely. After that first RubyConf, we reconnected while both attending Dick
Gabriel’s pilot MFA in Software Development program at UIUC in
early 2003. Avi’s been talking since then about running Ruby on a Smalltalk VM.
I’ve even started my own attempt once or twice, based on Avi’s ideas of how it could be done.
Given Avi’s interest in Ruby on Smalltalk and that he also created the mind-bending
Seaside web application framework, we invited him to keynote at last year’s RailsConf. It was there, in his message from the future keynote, that he made public
his belief that Ruby could benefit from being hosted on a mature, dynamic (Smalltalk) VM.
It was also, as I understand it, from that talk that Gemstone got the idea to run Rails.
The conversations started just after RailsConf last year, but it was only a few short months ago that Avi started work on Maglev. That’s part of what makes it so amazing. He and the
engineers at Gemstone have gotten a huge subset of the Ruby language running on the Gemstone VM in just three months.
Well, not really, but it’s fun to say.
There are a lot of things to like about what Maglev promises. By far the most interesting to me is
Gemstone’s persistence engine.
What’s coolest about how Gemstone’s persistence engine works within the context of Maglev is that it doesn’t
feel like a persistence engine. It’s just objects. Everything’s just objects.
If you think about it, the average Rails application is a styled set of CRUD operations on top of an
object graph. That’s right, an object graph. The fact that most Rails applications are backed
by a relational database is a somewhat-necessary annoyance.
So in circumstances where you don’t NEED an RDBMS, why would you want to litter your pristine Ruby objects with SQL and other RDBMS-related work-arounds? If it were possible to simply instantiate objects and not have to think about the underlying storage implementation at all, wouldn’t that be better?
That’s what Gemstone (and, therefore, Maglev) gives you.
There were questions during the demo about ActiveRecord compatibility. To me, building in ActiveRecord
compatibility is worse than a waste of time. Sure, there are things in ActiveRecord which would be useful
regardless of the storage mechanism. Declarative relationships and validations are examples. But, when
you’re dealing with objects in memory, the idea of a :conditions clause with SQL in it is absolutely
unnecessary and unappealing.
Fast as hell
Avi and the Gemstone people knew from their understanding of how the VM works that a Ruby implementation
on Gemstone would be really fast. They were right. But as I said, the speed of the implementation is
secondary to the persistence engine.
That being said, it’s really really fast. On micro-benchmarks, it’s up to 100 times faster than MRI.
As has already been whined about ad nauseam, micro-benchmarks can be misleading. They test very specific
parts of the implementation and don’t always give you a picture of what real-world application performance
will be like. So, let’s take this approach with the Maglev benchmarks: it’s fast enough. It’s probably a
lot faster than MRI. And, we’ve been using MRI for years for real applications.
Good enough. Probably awesome. But at least good enough.
Now is it going to slow down as they start implementing more of the libraries and language features? That’s
the conventional wisdom. I say no.
Smalltalk and Ruby are, as Avi has said numerous times, essentially the same language. So the Gemstone VM
has been tailor-made for running dynamic language code with closures, continuations, etc. and has been
doing it for years. Imagine the process, then, of converting Ruby to Smalltalk. It’s in most cases
a fairly straightforward language to language translation.
Where it isn’t as simple as that, Gemstone have a pretty big advantage: they own the VM and they can
change it to fit what Ruby needs.
I expect Maglev to get faster as the team starts to spend time on optimization. So far, they’re in the
“make it run” phase of the process. Remember, three months in.
Antonio Cangiano also had a look at Maglev recently and has a bit more to say about the specifics of Maglev performance
Ruby Compliance (or “it runs WEBRick!”)
So what’s next for Maglev? As the Gemstone team has said, their next goal is to start running and passing
the Ruby specs created by the other Ruby implementers. They hadn’t prioritized this leading up to RailsConf,
because, RailsConf being a web development conference, they wanted us all to see WEBRick running.
But, hey, they have WEBRick running! Have you looked at the code for WEBRick? That’s a lot of Ruby.
I’m looking forward to a report on how well the Ruby specs run at this moment. I think everyone will be
pleasantly surprised. And the specs will give the team a clear goal to work toward.
So Will I Use This Thing?!
When you don’t NEED an RDBMS (more often than you think) or you need scalable Ruby servers, I think
Maglev is going to be an enticing alternative. It’s not going to kill the other implementations. Each
implementation has its place. This isn’t a war, after all.
Macruby, JRuby, and IronRuby are for integration. MRI/YARV and Rubinius will compete for the “standard” use
cases. Maglev is for big, distributed object stores inside of fast, scalable servers. Think Rails,
Adhearsion, or various coordination services running custom protocols on sockets. Don’t run scripts in
Maglev. Don’t write desktop apps in Maglev. Just use Maglev to serve tons of requests against billions of
Maglev is good for the Ruby ecosystem just as MRI/YARV, Macruby, JRuby, and IronRuby are good for the
Ruby ecosystem. The fact that we (will) have so many alternatives is a good thing.