thanks for your answer，I know the necessity of key for compacted topics，and as you know，__consumer_offsets is a internal compacted topic in kafka，and it’s key is a triple of <groupid, topic, partition>，these errors are occurred when the consumer client wants to commit group offset. so why does his happen？
> 在 2016年7月19日，上午1:27，Dustin Cote <dus...@confluent.io> 写道： > > Compacted topics require keyed messages in order for compaction to > function. The solution is to provide a key for your messages. I would > suggest reading the wiki on log compaction. > <https://cwiki.apache.org/confluence/display/KAFKA/Log+Compaction> > > On Mon, Jul 18, 2016 at 12:03 PM, Kafka <kafka...@126.com> wrote: > >> Hi, >> The server log shows error as belows on broker 0.9.0. >> ERROR [Replica Manager on Broker 0]: Error processing append >> operation on partition [__consumer_offsets,5] (kafka.server.ReplicaManager) >> kafka.message.InvalidMessageException: Compacted topic cannot accept >> message without key. >> >> Why does this happen and what’s the solution? >> >> >> > > > -- > Dustin Cote > confluent.io
