Troubleshooting KSQL – Part 1: Why Isn’t My KSQL Query Returning Data?
Blog post from Confluent
The text provides an in-depth guide on troubleshooting common issues encountered when using KSQL, a SQL streaming engine for Apache Kafka. It highlights the problem of KSQL queries not returning data and explains various potential reasons, such as incorrect topic names, data not being present in the source Kafka topic, or KSQL reading from the latest offset by default. The article suggests using tools like kafkacat to verify the presence of data in Kafka topics and advises changing the offset setting to 'earliest' to read all existing data. It also touches on serialization issues, emphasizing the need for correct serialization and deserialization formats, and illustrates how malformed messages can lead to incomplete data retrieval. Additionally, it covers the importance of setting the correct key when declaring tables in KSQL to ensure data is returned, and provides troubleshooting tips for resolving these and other related issues.
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