On time and art

I was looking at one of my favorite works of art recently and realized that it reminds me a lot of the concept of time in distributed systems. The melting clocks are a great illustration for the fact that the notion of time as we understand it makes little sense in a distributed system where each node has its own physical clock that runs independently of the other clocks. In a single node system one can look at timestamps to figure out the ordering of events. However, this concept breaks down for a multi-node system involving multiple clocks due to problems like clock skew. While several types of logical clocks have been created to solve this problem and help come up with causal ordering between events I think it is fascinating that time, something we pretty much take for granted everyday, is something you cannot rely on anymore in a distributed system. This was one of the first problems I was exposed to while studying distributed systems and understanding how one can solve it was extremely intellectually satisfying.

Aside – in the past few years I’ve discovered that I’m a fan of surreal art. Another artist I quite like is Rene Magritte, with The Son of Man, The Human Condition, and The Treachery of Images being my favorite works by him.

On Zab

Apache ZooKeeper has become an indispensable component for many distributed systems: Apache Hadoop, Apache Mesos, Apache Kafka, Apache HBase, etc. all use ZooKeeper in some form or the other. I’ve written code that interacts with ZooKeeper and I’m a big fan of the simple APIs and powerful guarantees it provides.

I had a vague idea of the broadcast protocol that powers ZooKeeper but wasn’t awake of the details. So this weekend I decided to read a short paper that gives an overview of Zab (a more detailed description of Zab can be found in “Zab: High-performance broadcast for primary-backup systems” by Flavio P. Junqueira, Benjamin C. Reed, and Marco Serafini).

The title of the paper is extremely accurate – Zab is a very simple protocol that is intuitive and easy to understand. The paper does a great job of explaining the core concepts of the algorithm to the reader. I particularly liked section 3, which includes a comparison between Zab and Paxos. Section 4 is probably the most important section of the paper and is very well written. The figures illustrating the two main failure scenarios are a nice touch.

Next step – read the detailed Zab paper.

Let’s Go.

One of my goals of 2014 was to learn a new programming language, and for various reasons I decided on Go. While my learning progress has been pretty terrible for most of the year, I was able to make pretty good progress this week.

(Chart generated using the awesome pygal library. Code can be found here.)

Screen Shot 2014-09-28 at 11.09.48 AM

What made me get to 40% this month? Several things, but by far the most important one was A Tour of Go.

The tour is a fantastic resource for a person beginning to learn Go. It does a great job of explaining the important language features and constructs, and lets you try Go without having to install Go on your machine. This ability to try Go without having to install Go locally and setup your environment is incredibly powerful (this is how it works under the hood) and is something that I wish more languages incorporated into their websites. With the ability to compile almost anything down to Javascript one does not even have to build a remote sandbox environment (though that is more powerful and robust in my opinion) in order to introduce newcomers to your language.
I feel that the Tour could be improved by adding three things – syntax highlighting to the code in the console, more exercises, and including solutions to the exercises. Apart from that, I think it is a perfect learning resource.

My thoughts on Go? I think it is an interesting language, and something that I will most certainly delving into more. I’d read some Go code before (mostly Docker code) so I was vaguely aware of what the language looked like. I was initially a bit hesitant about the fact that Go has both high level (e.g. functional programming) and low level (e.g. pointers) features, but I think I quite like this ability to have and use both. The concurrency primitives look excellent, and I can’t wait to write some code using it. Another thing that scared me a little was the lack of classes, but structs + interfaces seem to be powerful enough to deal with that. I’ve read online about Go’s lack of generics being a problem, but I haven’t written enough code in Go to comment on this issue. I really liked the fact that the Go compiler doesn’t allow you to compile code that has unused imports or unused variables.

Next steps – read Go by Example and An Introduction to Programming in Go, and begin writing Go code to implement the two phase commit protocol.

Unresolved Resolutions

At the start of 2014 I wrote a post about what my goals were for this year. Now that we are 9 months in I thought it would be good to see how much progress I’ve made. And yes, I do agree that I should have done this 6 months in.

(Charts generated using the awesome pygal library. Code can be found here.)

  1. Learning Go – 10% progress has been made on this. I got distracted by various other things happening in life and forgot about this endeavor. I think I can still achieve this.

    Screen Shot 2014-09-10 at 10.27.51 PM

  2. Reading three research papers a month – I’m disappointed that I haven’t been able to keep up with this. While I have read a lot of research papers this year, it falls short of my goal of three a month. Papers I have read include Omega, Orleans, Photon, Raft, Paxos Made Simple, and F1.

    Screen Shot 2014-09-10 at 10.29.06 PM

  3. Blog more – My original post was pretty ambiguous by what I meant by “more”. Let’s assume “more” meant 4 posts a month. I’m tempted to make a POST related joke here but I won’t.

    Screen Shot 2014-09-10 at 10.32.38 PM

  4. Play guitar for at least 30 minutes a day – I think I’m averaging 20 minutes a day.
  5. Work out 6 days a week and start running again – Achieved minus the running. I’m definitely going to make up for that in the last 4 months though.