自己本地写了一个kafka的demo，起了一个消费者
@KafkaListener(topics = KafkaConstants.SMS_TOPIC_NAME, groupId = "sms")
public void listenGroup(ConsumerRecord record, Acknowledgment ack){
String value = record.value();
System.out.println("value1:" + value);
System.out.println("record1:" + record);
SmsThreadPool.submit(value);
ack.acknowledge();
}
但是如果过两天，offset就会从0开始重新消费。
解决见kafka官方文档https://kafka.apache.org/documentation.html#upgrade
offsets.retention.minutes
After a consumer group loses all its consumers (i.e. becomes empty) its offsets will be kept for this retention period before getting discarded. For standalone consumers (using manual assignment), offsets will be expired after the time of last commit plus this retention period.
Type: int Default: 10080 Valid Values: [1,...] importance: high Update Mode: read-only
当一个消费组的所有消费者断开链接后，offset的位移量会保留的时间，默认10080分钟，即7天。
Notable changes in 2.0.0
- KIP-186 increases the default offset retention time from 1 day to 7 days. This makes it less likely to "lose" offsets in an application that commits infrequently. It also increases the active set of offsets and therefore can increase memory usage on the broker. Note that the console consumer currently enables offset commit by default and can be the source of a large number of offsets which this change will now preserve for 7 days instead of 1. You can preserve the existing behavior by setting the broker config offsets.retention.minutes to 1440.
2.0.0版本之后，默认值是7天，之前版本是1天。
我的本地版本是1.0.1，所以保留时间是1天，推测是2天后启动，offset就被重置了。
所以安全起见，修改配置文件，将offsets.retention.minutes=10080，与log.retention.hours默认的168（7天）一致。文件路径：kafka/config/server.properties
