不多说，直接上干货！
一切来源于官网
http://kafka.apache.org/documentation/
Commit Log
提交日志
Kafka can serve as a kind of external commit-log for a distributed system. The log helps replicate data between nodes and acts as a re-syncing mechanism for failed nodes to restore their data. The log compaction feature in Kafka helps support this usage. In this usage Kafka is similar to Apache BookKeeper project.
kafka可以作为一种分布式的外部提交日志，日志帮助节点之间复制数据，并作为失败的节点来恢复数据重新同步，
kafka的日志压缩功能很好的支持这种用法，这种用法类似于Apacha BookKeeper项目。