When protocol is set to avro or canal-json, messages are sent per row change. A single Kafka message contains only one row change and is generally no larger than Kafka’s limit. Therefore, there is no need to limit the size of a single message. If the size of a single Kafka message does exceed Kakfa’s limit, refer to Why does the latency from TiCDC to Kafka become higher and higher?.
When protocol is set to open-protocol, messages are sent in batches. Therefore, one Kafka message might be excessively large. To avoid this situation, you can configure the max-message-bytes parameter to control the maximum size of data sent to the Kafka broker each time (optional, 10MB by default). You can also configure the max-batch-size parameter (optional, 16 by default) to specify the maximum number of change records in each Kafka message.