Software Engineering at Cxense

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A year ago I wrote a post about the things I have learned during my PhD at NTNU. Since then I wanted to write about my experience as a Software Engineer at Cxense. I am sure that the list of what I have learned over the past four and half years would be very long, so instead I would like to summarize it as the five best things about working at Cxense. So here it goes:


Engineers love tough problems and here are plenty of them. Within a month after starting at Cxense, I have been thrown into designing a weighting function that would include dwell time and page popularity into computing the impact of the page’s content on a user’s interest profile and implementing complex filters for a distributed low-level database (solved by implementing bit-wise logical filters and a stack machine). At the same time I reviewed a highly impressive implementation for an incremental inverted index on top of a compressed integer list and lots of mind-numbing bit-twiddling code. The author was Erik Gorset, whom I am deeply grateful for all the inspiration and advice over the years. Since then my colleagues and I have worked on thousands of dazzling problems within areas of distributed databases, data mining, machine learning and development operations, not to mention all bugfixes. Fixing bugs is actually fun, because it feels good to trace that flaw by the end of the day and fix it. Nothing is perfect, and that is also why you need to write good unit and integration tests. Writing tests is hard and time consuming, but it always pays off in the long run. Code reviews provide a great opportunity to learn how other people think and tackle challenges, both for the reviewer and the one being reviewed.


When I met guys from Cxense for the first time five years ago, they were going live with a large publisher network in Spain. I remember seeing a live chart with the event traffic instantly increasing ten times or so. The guys were very excited about whether the system would handle the challenge, and it did. Since then the numbers have increased by many orders of magnitude. We passed the 20 billion page views per month mark a two years ago. Counting all possible type of events we collect that would be above 60 billion events per month or more than one terabyte of data per day. Crawling is also approaching 100 million Web pages per month these days. These numbers are huge, but the transition impresses me even more because it is impossible to design a system for this kind of growth. A solution that is sufficient at one point has to be phased with a better solution at another point, which in its turn will become obsolete at a later point. Nevertheless, despite this tremendous growth we are still able to serve real-time data with latency counted in just milliseconds.


We used Java since the beginning, and previously most of us used Eclipse with a common setup for CheckStyle and FindBugs. Nowadays, the majority is using IDEA, but we still heavily rely on a common code style, static checks and a set of best practices. We use git with a common code repo and another repo for data center configuration related stuff. At the moment we use GitLab for code reviews and a homemade builder doing speculative merge builds and lots of awesomeness like stability tests and automatic deployment to the staging environment. Skipping the details, what I love most is that we can deploy anything within just a few minutes even at the current scale.

Initially we would rent hardware and run things on bare Ubuntu servers ourselves, using Upstart for continuous services and crontab for scheduled tasks. The implementation would be in Java with a BASH or Python wrapping and most of the internal services would often have a fixed HTTP port with JSON input/output. Data pipelines would often be implemented with a few simple of components, one of which would for example receive data and write it to disk using atomic appends, while another would tail the written data and crunch it or send it to another service (again using JSON over HTTP). This gave us many nice benefits for scaling (add more consumers behind a load balancer), failover (as long the data is written to disk somewhere, nothing is lost), debugging (just look up the logs) and monitoring.

With the growth mentioned earlier, we are now moving over to Mesos (running on top of our own hardware) and running things with Aurora. Nowadays, we use gRPC for communication between services, Consul for service discovery, Prometheus for performance metrics and alerting and Grafana for monitoring dashboards. Things are getting even better and deployments across multiple data centers and hundreds of machines are still within minutes. In fact, they are only getting faster.


When I started at Cxense, it was a typical startup – we used JIRA for issue tracking, but it was a mix of roadmap features, devs’ own ideas and FIXMEs, support issues reported by customers or deliverables promised by sales guys, with no clear definition for priorities or deadlines. We would pick tickets that we thought were most urgent or important and did our best to solve them most efficiently. We would discuss this in daily standups and perhaps present some cool new features at regular video calls. Once in a while each developer would have a hell week, when he or she would be facing all the incoming support issues, chats and alerts. The fun part in this was that one could hack a set of new features over a weekend or handle a hundred of support issues during a hell week. The boring part of this was figuring out where the company was going after all.

Today everything is much more organized. For the feature part, we have a roadmap for a year ahead, which then drains down to specific plan for each quarter for each team. For the support part, we have several lines of highly trained professionals, which filter out all the noise and leave only actual issues to be fixed. For most teams, we run two-week iterations, where tickets come from the development roadmap for the given quarter, pre-triaged support issues meeting the bar, or the technical roadmap issues. The last part covers things like scalability improvements, shifting out components with better alternatives, or making the system more resilient. We separated on-call incidents from the rest of the JIRA issues long time ago, but for the last year or so we have also been working on growing a highly skilled infrastructure team.

Each iteration starts with a planning phase involving team leads and engineering managers, followed by a meeting where team members are free to pick the issues they like to put their hands on and with respect to the amount of work they can handle in the next sprint. The sprint ends with a highlight of the most important things a team has achieved and a demonstration of the most interesting features.


The most important ingredient in a great workplace is people. Joining Cxense I had no expectations other that here would be the best people in the industry. This turned out to be true, and I am lucky to be working with some of the best engineers and business experts in the field. It is a pleasure to be a part of the discussions and changes we have done over the years and those to come.

Cxense is spread across 5 out of the 7 parts of world. Therefore, it is quite common that my day would start with a quick fix for a support issue from Tokyo, followed by a few quick answers to questions from my colleagues in Samara, Munich, Buenos Aires or San Francisco. The changes I made the day before would be reviewed by a colleague sitting next to me in Oslo and then distributed to the data centers across the world. After the lunch I would focus on the next feature, working with the data from a major news publisher in USA, Argentina, Norway or Japan. On the way home, I would comment on the global company chat and receive a funny cat picture from a colleague in Melbourne. The world is very small when it comes to Cxense.

In conclusion

Cxense grew a lot over the years I have been working here, but it remains a fast-paced company with talented people, exciting challenges and a cool software stack. Things are getting better and I can only imagine where we will be in the next five years. While working here I have learned a billion things about software development (and yet still learning), and I hope that this post was able to bring some of those insights to you. …ah, and by the way, we are hiring!

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