ge: (00440, Message_00440) at offset 218
Received message: (00443, Message_00443) at offset 219
org.apache.kafka.common.errors.NetworkException: The server disconnected before a response was received.
org.apache.kafka.common.errors.NetworkException: The server disconnected before a response was received.
org.apache.kafka.common.errors.NetworkException: The server disconnected before a response was received.
org.apache.kafka.common.errors.NetworkException: The server disconnected before a response was received.
org.apache.kafka.common.errors.NetworkException: The server disconnected before a response was received.
org.apache.kafka.common.errors.NetworkException: The server disconnected before a response was received.
org.apache.kafka.common.errors.NetworkException: The server disconnected before a response was received.
Received message: (00442, Message_00442) at offset 222
Send message: (00452, Message_00452) at offset 223 to partition(1) in 7492 ms
Send message: (00454, Message_00454) at offset 224 to partition(1) in 7485 ms
Send message: (00455, Message_00455) at offset 225 to partition(1) in 7482 ms
Send message: (00458, Message_00458) at offset 226 to partition(1) in 7473 ms
Send message: (00460, Message_00460) at offset 227 to partition(1) in 7467 ms
Send message: (00461, Message_00461) at offset 228 to partition(1) in 7465 ms
Send message: (00462, Message_00462) at offset 229 to partition(1) in 7462 ms
Send message: (00463, Message_00463) at offset 230 to partition(1) in 7459 ms
Send message: (00464, Message_00464) at offset 231 to partition(1) in 7456 ms
Send message: (00465, Message_00465) at offset 232 to partition(1) in 7453 ms
......
Send message: (01103, Message_01103) at offset 543 to partition(1) in 5478 ms
Received message: (00631, Message_00631) at offset 310
Received message: (00633, Message_00633) at offset 311
Send message: (00451, Message_00451) at offset 220 to partition(0) in 7525 ms
Received message: (00634, Message_00634) at offset 312
Send message: (00453, Message_00453) at offset 221 to partition(0) in 7518 ms
Received message: (00639, Message_00639) at offset 313
Send message: (00456, Message_00456) at offset 222 to partition(0) in 7509 ms
Received message: (00641, Message_00641) at offset 314
Send message: (00457, Message_00457) at offset 223 to partition(0) in 7506 ms
Received message: (00643, Message_00643) at offset 315
......
出现错误的时候，Producer 抛出了 NetworkException 异常。其中有3589条 Received 日志，3583条 Send 日志，7条 NetworkException 异常日志，发送消息的最大序号是3590，接收消息的最大序号是3589，有以下几个值得注意的地方，
- 宕机之前，消息的接收并不是顺序的，这是因为 topic1 有2个分区，Kafka 只保证分区上的有序；
- 宕机之后，出现了长段的发送日志而没有接收日志，说明 Kafka 此时正在选举，选举的过程会阻塞消费者；
- 从接收消息的条数和序号来看，所有的消息都收到了，没有丢（没有收到3590的消息可能是因为强制退出 client 进程的原因），发送的过程的7个异常应该只是虚警，7条异常对应序号444~450，3583条 Send 消息再加上这7条，与总消息3590条一致；
从这个实验中，可以看到，虽然 Kafka 不保证消息重复发送，但是却在尽量保证没有消息被重复发送，可能我的实验场景还不够极端，没有做出消息重复的情况。
如之前所说，如果要保持完全顺序性，需要使用单分区；如果要避免抛出 NetworkException 异常，就使用 Producer 同步发送。下面，我们重做上面的例子，不同之处是使用单分区和 Producer 同步发送，截取一段 Broker 宕机时的日志如下，
......
Sent message: (118, Message_00118)
Received message: (00118, Message_00118) at offset 117
Received message: (00119, Message_00119) at offset 118
Sent message: (119, Message_00119)
Sent message: (120, Message_00120)
Received message: (00120, Message_00120) at