Apache Flink: could not find implicit value for evidence parameter of type This is a common error when transforming streams in Apache Flink based applications. The solution is simple. We just need to import the following: Which should import the necessary types for the operations.
Apache Flink: History Server One of the problems we have faced running Apache Flink that we have a very limited windows for getting access to the details about failed / crashed jobs. The job details just disappear and cannot be retrieved especially form web front end. Here is how it looks like: Actually we are… Continue reading »
com.esotericsoftware.kryo.KryoException: Unusual solution upgrading Flink While upgrading from Flink from 1.4 to a newer version 1.6.1, there are a few build issues. After we fix the issues, suddenly we started getting KryoException. Why are we getting this and how it this related to the upgrade? Let’s start with the exception message. If you try to… Continue reading »
Apache Flink – mapWithState on KeyedStream mapWithState operator provides a syntactic ease for keeping ValueState for map operations on KeyedStreams in Apache Flink. It is specially useful for doing a running count on the data. That is exactly what we are going to try in this post. Just remember that you don’t have to return… Continue reading »
Downloading Flink You can download flink from it’s Apache’s site. We are downloading Flink 1.6, which is the latest version available. https://flink.apache.org/downloads.html It requires Java version 8. Running Flink Cluster Let’s start the cluster. We can just run it directly from bin folder using start-cluster.sh utility available with the download. Alternatively we can run it… Continue reading »
Apache Flink – Collections & Streams While developing a streaming application, it is often necessary to use some inputs as collections. This can be specially useful for testing purposes. In this post we are trying to discuss how we can create a DataStream from a collection. After applying some operators on the stream, we are… Continue reading »