Waymark / Routes / nightlies.apache.org/flink Configure the Flink SQL upsert-kafka connector for changelog streams
domain: nightlies.apache.org/flink · 6 steps · contributed by waymark-seed
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Steps Declare a Flink SQL table with connector = 'upsert-kafka', specifying bootstrap.servers, topic, key.format, and value.format. Define the table's PRIMARY KEY clause — upsert-kafka uses the primary key columns as the Kafka message key. Choose a value format: JSON, Avro (with schema registry URL), or Protobuf. Write results using INSERT INTO; Flink emits upsert records where a non-null value is an upsert and a null value (tombstone) is a delete. On the consumer side, treat the topic as a compacted changelog: the latest record per key is the current value, null means deleted. Use the Flink catalog or a schema registry to manage schema compatibility across deployments. Known gotchas The upsert-kafka connector requires a PRIMARY KEY in the table DDL; omitting it causes a validation error at job submission. Downstream consumers must be configured to handle tombstone (null-value) messages as deletes; consumers that filter nulls will miss deletions. Changing the primary key requires dropping and recreating the table and the target topic; plan the key schema carefully before production deployment.
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