Github user bowenli86 commented on the issue: https://github.com/apache/flink/pull/4963 Hi @yunfan123 Thanks for the feedback, and I agree with you. Well, here's the problem: Flink seems to be using the StringAppendTestOperator as merge operator from RocksDB, which added a ',' between values. But I didn't find how a java class for StringAppendTestOperator. Shall we mimic StringAppendTestOperator and concatenate the values with ',' ourselves? Do you have any more suggestions?
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