• Large Teams: Finding A Green Build

    I work on a large engineering team. The main Slack channel for our engineering department has 425 people in it. The code base is split into many repositories, dominated by a big Ruby on Rails application with many contributors. At the time of writing, the last 1,000 commits in master on that repository where made by 169 contributors.

    The continuous integration for said mono-repo is heavily parallelized but still takes ~30 minutes to complete. Occasionally, a branch is merged that causes the build to fail. Usually, the case is that the specs worked correctly for that branch (otherwise we can’t merge), but new changes in master are not compatible. As hard as the team tries to maintain a green build (i.e. a build that passes and is deployable), a red build is somewhat frequent.

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  • The REPL: Issue 62 - October 2019

    The Night Watch

    In this article James Mickens writes about being a systems programmer. The writing is witty and funny. It’s not new, but it is new to me. A few choice quotes:

    One time I tried to create a list<map>, and my syntax errors caused the dead to walk among the living. Such things are clearly unfortunate.

    Indeed, the common discovery mode for an impossibly large buffer error is that your program seems to be working fine, and then it tries to display a string that should say “Hello world,” but instead it prints “#a[5]:3!” or another syntactically correct Perl script

    However, when HCI people debug their code, it’s like an art show or a meeting of the United Nations. There are tea breaks and witticisms exchanged in French; wearing a non-functional scarf is optional, but encouraged.

    Do you see the difference between our lives? When you asked a girl to the prom, you discovered that her father was a cop. When I asked a girl to the prom, I DISCOVERED THAT HER FATHER WAS STALIN.

    Empathy is a Technical Skill

    Andrea Goulet writes an interesting article about empathy. The takeaway is that technical-minded folks should think of empathy as a skill that can be learned, and used effectively to achieve your aims. From experience, I can attest that increasing your empathy is like having a super power.


    This project looks really promising. It formats the output of Postgres EXPLAIN ANALYZE as a flame graph, which can help in figuring out which parts of your queries are worth digging into.

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  • The REPL: Issue 61 - September 2019

    Building A Relational Database Using Kafka

    Robert Yokota explores building a relational database on top of Kafka. It follows his previous article on creating an in-memory cache on backed by Kafka. RDBM systems are commonly thought of keeping track of tables and rows. The semantics of SQL reinforce the concept of rows being updatable. In practice though, most implementation use an immutable log under the hood. That is what makes transactions possible, each with its own consistent view of the world. Kafka can be thought of as an “exposed” MVCC system, and the current state of the data can be derived by consuming the messages in a topic. The article is interesting in that it assembles a relation database by using different existing open-source projects.

    3 Key Ideas Behind The Erlang Thesis

    Yiming Chen summarizes Joe Armstrong’s thesis: “Making reliable distributed systems in the presence of software errors”. The 3 key ideas identified: Concurrency oriented programming, abstracting concurrency, and let-it-fail philosophy. Armstrong is Erlang’s creator, and his thesis has been very influential in the Erlang and Elixir communities.

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  • The REPL: Issue 60 - August 2019

    Issue 60! I’ve been posting my favorite links to tech articles every month for the last 5 years! I’ve linked to 163 articles in that time (not including the links in this post). And, now that I am looking back… I realize that I’ve made a mistake and I re-used #53 for the 2018-12 and 2019-12 issues. ¯\_(ツ)_/¯

    Engineers Don’t Solve Problems

    This article by Dean Chahim is not about software engineering or computer science. It’s about Mexico City’s infrastructure and the decades-long battle to prevent flooding in the city. The article stroke a chord with me: Mexico City is my home town, it’s where I went to University to obtain my degree in Civil Engineering. The article illustrates how engineers make trade-offs that might have far-reaching consequences, and are not immune from political and socio-economic influence. There are lessons there for all engineers.

    How to Build Good Software

    Software has characteristics that make it hard to build with traditional management techniques; effective development requires a different, more exploratory and iterative approach.

    Li Hongyi writes a thoughtful article on why software projects are not the same as other engineering projects, and require different management techniques. Successful software projects are very iterative and oscillate between cycles discovery and consolidation.

    Arcs of Seniority

    Stevan Popovic breaks down engineering seniority into a few factors: Independence, authority, Design, and Influence. During once career each of these develops in an engineer, and mark different types of seniority. As expected, not everyone reaches the same maturity in all factors at once. Each senior engineer has it’s own mix. The illustrations on the articles are particularly helpful.

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  • Spring Hopes Eternal

    I have a love-hate relationship with spring, Rails’ application pre-loader. One one hand, it speeds up the feedback loop when doing TDD. Faster running specs, promote running them more often, which promotes writing code in smaller increments, and so forth. On the other hand, it is dark magic: In its quest to be unobtrusive, it starts automatically, and barely reports it’s being used at all. Occasionally it looses track of which code it needs to reload, causing much confusion to the user, as the code executing is different than the version saved on disk.

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