Mar 10, 2025

Data Wrangling with Flink SQL

The UK Government publishes a lot of its data as open feeds. One that I keep coming back to is the Environment Agency’s flood-monitoring API that gives access to an estate of sensors that provide information about data such as river levels and rainfall.

The data is well-structured and provided across three primary API endpoints. In this blog article I’m going to show you how I use Flink SQL to explore and wrangle these into the kind of form from which I am then going to build a streaming pipeline using them.

Mar 6, 2025

Joining two streams of data with Flink SQL

There was a useful question on the Apache Flink Slack recently about joining data in Flink SQL:

How can I join two streams of data by id in Flink, to get a combined view of the latest data?

Mar 3, 2025

How to explode nested arrays with Flink SQL

Let’s imagine we’ve got a source of data with a nested array of multiple values. The data is from an IoT device. Each device has multiple sensors, each sensor provides a reading.

Mar 15, 2024

Apache Flink talks at Kafka Summit London 2024

This year Kafka Summit London includes a dedicated track for talks about Apache Flink. This reflects the continued rise of interest and use of Apache Flink in the streaming community, as well as the focus that Confluent (the hosts of Kafka Summit) has on it.

I’m looking forward to being back at Kafka Summit. I will be speaking on Tuesday afternoon, room hosting on Wednesday morning, and hanging out at the Decodable booth in between too.

Here’s a list of all the Flink talks, including the talk, time, and speaker. You find find more details, and the full Kafka Summit agenda, here.

Nov 16, 2023

Learning Apache Flink S01E06: The Flink JDBC Driver

As a newcomer to Apache Flink one of the first things I did was join the Slack community (which is vendor-neutral and controlled by the Flink PMC). At the moment I’m pretty much in full-time lurker mode, soaking up the kind of questions that people have and how they’re using Flink.

One question that caught my eye was from Marco Villalobos, in which he asked about the Flink JDBC driver and a SQLDataException he was getting with a particular datatype. Now, unfortunately, I have no idea about the answer to this question—but the idea of a JDBC driver through which Flink SQL could be run sounded like a fascinating path to follow after previously looking at the SQL Client.

Oct 25, 2023

Learning Apache Flink S01E05: Installing PyFlink (with some bumps along the way…)

When I started my journey learning Apache Flink one of the things that several people expressed an interest in hearing more about was PyFlink. This appeals to me too, because whilst Java is just something I don’t know and feels beyond me to try and learn, Python is something that I know enough of to at least hack my way around it. I’ve previously had fun with PySpark, and whilst Flink SQL will probably be one of my main focusses, I also want to get a feel for PyFlink.

The first step to using PyFlink is installing it - which should be simple, right?

Oct 10, 2023

Learning Apache Flink S01E04: A [Partial] Exploration of the Flink SQL Client

So far I’ve plotted out a bit of a map for my exploration of Apache Flink, looked at what Flink is, and run my first Flink application. Being an absolutely abysmal coder—but knowing a thing or two about SQL—I figure that Flink SQL is where my focus is going to lie (I’m also intrigued by PyFlink, but that’s for another day…).

Oct 5, 2023

Learning Apache Flink S01E03: Running my First Flink Cluster and Application

🎉 I just ran my first Apache Flink cluster and application on it 🎉

Oct 2, 2023

Learning Apache Flink S01E02: What is Flink?

My journey with Apache Flink begins with an overview of what Flink actually is.

What better place to start than the Apache Flink website itself:

Apache Flink is a framework and distributed processing engine for stateful computations over unbounded and bounded data streams. Flink has been designed to run in all common cluster environments, perform computations at in-memory speed and at any scale.

Sep 29, 2023

Learning Apache Flink S01E01: Where Do I Start?

Like a fortunate child on Christmas Day, I’ve got a brand new toy! A brand new—to me—open-source technology to unwrap, learn, and perhaps even aspire to master elements of within.

I joined Decodable two weeks ago, and since Decodable is built on top of Apache Flink it seems like a great time to learn it. After six years learning Apache Kafka and hearing about this “Flink” thing but—for better or worse—never investigating it, I now have the perfect opportunity to do so.