【Kafka十一】关于Kafka的副本管理

snake_l

1. 关于request.required.acks
　　request.required.acks控制者Producer写请求的什么时候可以确认写成功，默认是0，
　　0表示即不进行确认即返回。
　　1表示Leader写成功即返回，此时还没有进行写数据同步到其它Follower Partition中
　　-1表示根据指定的最少Partition确认后才返回，这个在
　　This value controls when a produce request is considered completed. Specifically, how many other brokers must have committed the data to their log and acknowledged this to the leader? Typical values are

• 0, which means that the producer never waits for an acknowledgement from the broker (the same behavior as 0.7). This option provides the lowest latency but the weakest durability guarantees (some data will be lost when a server fails).
  
• 1, which means that the producer gets an acknowledgement after the leader replica has received the data. This option provides better durability as the client waits until the server acknowledges the request as successful (only messages that were written to the now-dead leader but not yet replicated will be lost).
  
• -1, The producer gets an acknowledgement after all in-sync replicas have received the data. This option provides the greatest level of durability. However, it does not completely eliminate the risk of message loss because the number of in sync replicas may, in rare cases, shrink to 1. If you want to ensure that some minimum number of replicas (typically a majority) receive a write, then you must set the topic-level min.insync.replicas setting. Please read the Replication section of the design documentation for a more in-depth discussion
  

2. 关于min.insync.replicas
　　When a producer setsrequest.required.acks to -1, min.insync.replicas specifies the minimum number of replicas that must acknowledge a write for the write to be considered successful. If this minimum cannot be met, then the producer will raise an exception (either NotEnoughReplicas or NotEnoughReplicasAfterAppend). When used together, min.insync.replicas and request.required.acks allow you to enforce greater durability guarantees. A typical scenario would be to create a topic with a replication factor of 3, set min.insync.replicas to 2, and produce with request.required.acks of -1. This will ensure that the producer raises an exception if a majority of replicas do not receive a write.
3. 关于Lead Partition和Follower Parttiion
　　Each partition has one server which acts as the "leader" and zero or more servers which act as "followers". The leader handles all read and write requests for the partition while the followers passively replicate the leader. If the leader fails, one of the followers will automatically become the new leader. Each server acts as a leader for some of its partitions and a follower for others so load is well balanced within the cluster.
　　也就是说，读写操作都是发生在每个Partition的Lead Partition上，Follower Partition只是用来做备份以便进行失败转移
4. default.replication.factor
　　每个Partition有几个副本，默认是1，即只有1个副本(即不做备份)