Jepsen worked with Buf to analyze the safety of Bufstream, a Kafka-compatible streaming system. We found three safety and two liveness issues in Bufstream 0.1.0, including the loss of acknowledged writes in healthy clusters. These problems were resolved by version 0.1.3. We also discovered serious issues in Kafka’s transaction protocol, including write loss, aborted read, and torn transactions. These problems affect Kafka, Bufstream, and (presumably) other Kafka-compatible systems; they remain outstanding.