I’ve been looking into handing a bit of our messaging infrastructure over to a managed alternative. Managing your own messaging infrastructure that should be highly available is not always an investment you want to make in this day and age. Going through the documentation and relying on experiences from some people I trust, I ended up looking at AWS and SNS/SQS. Making the Github repository rounds, looking for inspiration, I stumbled on JustSaying: a library by the people from JustEat implementing a message bus on top of AWS. ...

Seems that it’s impossible to beat the Gaussian curve of blogging frequency. On the other hand, I spent quite some of my mental blogging budget on an interview with InfoQ. I’m a bit bummed out that it’s such a large wall of text. When submitting the answers, I highlighted some snippets which should make for easier scanning. Too bad the formatting was lost when publishing it. I included some highlights below. ...

Writing doesn’t necessarily always come naturally to me. It often takes me days, weeks or even months of toying with an idea, before I think it’s mature enough to put it down into writing. I can’t afford that luxury this time though, I wouldn’t think of myself as much of a friend if Pieter didn’t get to read this in time. I met Pieter the first time in a bar in Vilnius, December 2013, I accidentally ended up sitting next to him during the traditional pre-conf drinks. The first thing that stood out, was what a comfortable warm sweater he was wearing - I still cherish the memory of that grey woolen sweater on cold winter nights. I’m still unsure whether it was the sweater or his undeniable radiant charisma that made its way into my memories. When Pieter talks, people tend to listen, or at least pay attention. That’s what I ended up doing that night - listening, sipping in the knowledge, afraid to make a fool out of myself joining the conversation. ...

In the oldest system I’m maintaining right now, we have an account aggregate that, next to mutating various balances, produces immutable financial transactions. These transactions are persisted together with the aggregate itself to a relational database. The transactions can be queried by the owner of the account in an immediate consistent fashion. The table with these transactions looks similar to this: CREATE TABLE [dbo].[Transaction] ( [Id] [int] IDENTITY(1,1) NOT NULL, [Timestamp] [datetime] NULL, [AccountId] [int] NOT NULL, [TransactionType] [varchar](25) NOT NULL, [CashAmount] [decimal](19, 2) NOT NULL, [BonusAmount] [decimal](19, 2) NOT NULL, [...] [...] () NULL /* Too much metadata I'm not very happy about */ CONSTRAINT [Tx_PK] PRIMARY KEY CLUSTERED ( [Id] ASC) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 100) ON [PRIMARY] ) ON [PRIMARY] There’s an index on the timestamp, the account identifier and the transaction type, which allows for fast enough reads for the most common access patterns which only return a small subset. ...

User notifications are a feature that came as an afterthought, but turned out to be rather easy to implement - without touching (read: breaking) existing functionality - thanks to having an immutable event log. In the domain I’m working in at the moment, we will often give users incentives to return to the website, or to extend their stay on the website. These incentives were only communicated by email at first, and this is a decent medium when you want users to return to the website. However, when you want to extend their stay on the website, you want to avoid users switching contexts between your website and their mail client. But also, as soon as they return to your website, you want to show them a crisp overview of all relevant calls to action. Having most calls to action map to a specific page, the list of notifications can serve as a one-click starting point, lowering the hurdle to browse to a relevant page. ...

Visualizing some data earlier this week I had to compute the running total of a sequence of numbers. For example, if the input sequence was [ 100; 50; 25 ] the result of the computation would be a new sequence of [ 100; 150; 175 ]. Muscle memory made me take a procedural approach, which works, but made me wonder if I could get away with less lines of code and without mutable state. ...

I started in 2014 to keep lists of everything I consume. I’ve continued this effort throughout 2015 and can now share the items I particularly enjoyed. In 2015, I read 16 books and 3 papers, watched 3 movies and 4 shows, listened to 1 audio book and no podcasts. A lot less TV compared to 2014, but most of that time went to playing video games with some of my friends. Also a lot less time spent in the car listening to audiobooks or podcasts, since I’m now dropping off my girlfriend every day. ...

In my recent talk on Evil by Design, I showed how I’ve been visualizing event streams as a means to get a better grip on how aggregates behave in production. The talk’s scope kept me from showing the code that goes together with the examples shown. Consider this post as an addendum to that talk. First off, we need a few types: a string that identifies a stream, an event containing a timestamp and its name. A stream which is a composition of an identifier and a sequence of events. We also need a function that’s able to read a stream based on its identifier. ...

Third time attending Build Stuff, first time doing a talk. I’m happy that it’s out of the way and can now just enjoy the conference, but I’m even more excited that it was well-received! The talk should have been recorded, but you can already find the abstract and slides below. Last year I ventured into the domain of (online) gambling. Given that the industry has been around since forever, I expected most problems to be of the technical kind. As it turned out, the struggle with technology was only part of a bigger problem; to move forward we needed to fully grasp the industry and its consumers. Events started out as a way to dismantle a legacy system, but quickly proved to be an effective tool to gain a deeper understanding of our domain. Visualising event streams, we discovered patterns that helped us identify what drives different types of users. Having a better understanding of what customers are looking for, we dove into existing literature to learn which techniques and models casinos use to cater for each type of user. We learned how to program chance while staying true to the Random Number God. Even when variance is brutal, casinos have enough data and tools to steer clear from the pain barrier. All of this entails interesting problems and software, but isn’t my code damaging society? Or is gambling just another human trait? ...

Casinos invest a lot of energy selling the dream. One way to do this is by showing off people winning big in your casino. Everyone has seen those corny pictures of people holding human-sized cheques right? It’s a solid tactic, since empirical evidence shows that after a store has sold a large-prize winning lottery ticket, the ticket sales increase from 12 to 38% over the following weeks. If we look at slot machine play, what exactly defines a big win? The first stab we took at this was quite sloppy. We took an arbitrary number and said wins bigger than 500 euro are impressive. This was quick and easy to implement, but when we observed the results we noticed that when you have players playing at high stakes, a win of 500 euro really isn’t that impressive, and we would see the exceptional high roller often dominate the results. ...