Hi, I was playing with the new producer in 0.8.2.1 using partition keys ("semantic partitioning" I believe is the phrase?). I noticed that the default partitioner in 0.8.2.1 does not partition items the same way as the old 0.8.1.1 default partitioner was doing. For a test item, the old producer was sending it to partition 0, whereas the new producer was sending it to partition 4.
Digging in the code, it appears that the partitioning logic is different between the old and new producers. Both of them hash the key, but they use different hashing algorithms. Old partitioner: ./core/src/main/scala/kafka/producer/DefaultPartitioner.scala: def partition(key: Any, numPartitions: Int): Int = { Utils.abs(key.hashCode) % numPartitions } New partitioner: ./clients/src/main/java/org/apache/kafka/clients/producer/internals/Partitioner.java: } else { // hash the key to choose a partition return Utils.abs(Utils.murmur2(record.key())) % numPartitions; } Where murmur2 is a custom hashing algorithm. (I'm assuming that murmur2 isn't the same logic as hashCode, especially since hashCode is overrideable). Was it intentional that the hashing algorithm would change between the old and new producer? If so, was this documented? I don't know if anyone was relying on the old default partitioner, as opposed to going round-robin or using their own custom partitioner. Do you expect it to change in the future? I'm guessing that one of the main reasons to have a custom hashing algorithm is so that you are full control of the partitioning and can keep it stable (as opposed to being reliant on hashCode()). Thanks, -James