The exponential cost of contention

I enjoy Nati Shalom's blog, although it always has that taste of having the agenda of pushing Gigaspace's solutions. But putting that aside his posts are always well thought-out and well written.

I think his latest blog on the Economies of Non-Scale really drive some points home about scalability, or more to the point, the cost of non-linear scalability.

If 90% of our application is free of contention, and only 10% is spent on a shared resources, we will need to grow our compute resources by a factor of 100 to scale by a factor of 10! Another important thing to note is that 10x, in this case, is the limit of our ability to scale, even if more resources are added.

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1. The cost of non-linearly scalable applications grows exponentially with the demand for more scale.

2. Non-linearly scalable applications have an absolute limit of scalability. According to Amdhal's Law, with 10% contention, the maximum scaling limit is 10. With 40% contention, our maximum scaling limit is 2.5 - no matter how many hardware resources we will throw at the problem

That's something to chew on. These are real costs, both to your business, to your users, and to the environment. Even if you only have a teeny 10% contention in your system, that 10% will nail you faster than you can say ACID semantics. And as has become very clear to me the final breaking point, the final point of contention in any traditional web application architecture, is the database. Get rid of that and you're home free.

How do you do that? Well, there are a lot of people trying to solve this problem with things like space-based architectures, eventual consistency, distributed map/reduce and Stonebraker's H-Store architecture. Anything to let each instance stand on its own and not have to serialize with the rest of the system at any point, in any form.

Some people argue that scalability is so hard that you shouldn't think about it until you need to. But I really believe that if you do enough to educate yourself and make some wise choices, you will be very glad you did.

What I'd like to see is the industry coalescing around some best practices, an open source "scale stack" ala LAMP, tools, community, and hosting environments like Amazon, that allow developers to easily build applications that will scale from the get go. That's where I want to see things go. That way you don't have to throw your hands up and hope for the best. Because as you can see, the costs can be deadly.

Something to think about...