Shulou(Shulou.com)06/01 Report--

Although MGR uses Slave's channel, it only uses the execution thread (Applier Thread) of this channel to execute Binlog Event, and does not use this channel to transmit Binlog Event. MGR does not use the Binlog Event transport mechanism of asynchronous replication, nor does it use the service port of MySQL for communication. MGR creates a separate TCP port for communication, through which Group Replication plug-ins on various MySQL servers are connected, and the two can communicate directly.

The transfer of Binlog Event is not a simple point-to-point transfer like asynchronous replication. MGR uses the Paxos protocol when transmitting data. Paxos protocol ensures the consistency and atomicity of data transmission. MGR constructs a distributed state machine replication mechanism based on Paxos protocol, which is the core technology to realize multi-master replication. This technology brings three main advantages to MGR, which are as follows.

Brain fissure does not occur in 1.MGR (but be aware that network partitions may occur, and MGR behaves slightly differently depending on the parameter group_replication_unreachable_majority_timeout=0/N setting).

2.MGR has good redundancy and can guarantee that Binlog Event is copied to at least half of the members. As long as no more than half of the members are down at the same time, it will not cause data loss.

3.MGR also guarantees that as long as the Binlog Event is not transferred to more than half of the members, the local members will not write the Binlog Event of the transaction to the Binlog file and commit the transaction, thus ensuring that there will be no data that does not exist on the online members of the group on the server that is down. Therefore, after the down server is restarted, you no longer need special processing to join the group.

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