> Problem: Sometimes after deploying the RocketMQ cluster, when you try to execute some commands of "mqadmin", the following exception will appear:
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Solution: Execute `export NAMESRV_ADDR=ip:9876` (ip refers to the address of NameServer deployed in the cluster) on the VM that deploys the RocketMQ cluster.Then you will execute commands of "mqadmin" successfully.
## 2. The inconsistent version of RocketMQ between the producer and consumer leads to the problem that message can't be consumed normally.
## 2 The inconsistent version of RocketMQ between the producer and consumer leads to the problem that message can't be consumed normally.
> Problem: The same producer sends a message, consumer A can consume, but consumer B can't consume, and the RocketMQ Console appears:
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Solution: The jar package of RocketMQ, such as rocketmq-client, should be the same version on the consumer and producer.
## 3. When adding a new topic consumer group, historical messages can't be consumed.
## 3 When adding a new topic consumer group, historical messages can't be consumed.
> Problem: When a new consumer group of the same topic is started, the consumed message is the current offset message, and the historical message is not obtained.
In some cases, the Consumer needs to reset the consume position to 1-2 days ago. At this time, on the Master Broker with limited memory, the CommitLog will carry a relatively heavy IO pressure, affecting the reading and writing of other messages on that Broker. You can enable `slaveReadEnable=true`. When Master Broker finds that the difference between the Consumer's consume position and the latest value of CommitLog exceeds the percentage of machine's memory (`accessMessageInMemoryMaxRatio=40%`), it will recommend Consumer to read from Slave Broker and relieve Master Broker's IO.
## 5. Performance
## 5 Performance
Asynchronous flush disk is recommended to use spin lock.
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Synchronous flush disk is recommended to increase the `sendMessageThreadPoolNums` appropriately. The specific configuration needs to be tested.
## 6. The meaning and difference between msgId and offsetMsgId in RocketMQ
## 6 The meaning and difference between msgId and offsetMsgId in RocketMQ
After sending message with RocketMQ, you will usually see the following log: