Troubleshooting KSQL – Part 1: Why Isn't My KSQL Query Returning Data? | Confluent

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This post details troubleshooting common issues encountered with KSQL, focusing on why a KSQL query might not return data. It outlines five primary reasons: no data in the source topic, no new data arriving, KSQL consuming from a later offset, data not matching predicates, and deserialization errors. The post provides practical diagnostic steps using KSQL commands (DESCRIBE EXTENDED, SET 'auto.offset.reset') and external tools like kafkacat to verify topic contents and offset configurations. It also touches on the importance of correct data formats and predicate logic.