Redis master-slave replication - mentality detection mechanism

The heartbeat detection

When synchronization is complete , The master slave server enters the command propagation phase , At this time, the master server should always send its own write commands to the server , As long as the slave server always receives and executes the write command sent by the master server , The data consistency of the master and slave servers can be ensured .

In the command propagation phase , From the server The default is once per second , To the primary server dispatch orders .

REPLCONF ACK <replication_offset>

REPLCONF ACK The command has three functions for the master and slave servers ：

• Check the network connection status of the master-slave server
• Aided implementation min-slaves Options

• Detection command lost

Detect the network connection status of the master-slave server

If the primary server doesn't receive from the server for more than a second REPLCONF ACK command , Then the primary server will think that there is something wrong with the connection .

Aided implementation min-slaves configuration option

Redis Of min-slaves-to-write and min-slaves-max-lag Two options prevent the primary server from executing write commands without security

Detection command lost

If it's due to a network failure , The write command propagated from the master server to the slave server is lost in half way , So when the slave server sends to the master server REPLCONF ACK<replication_offset> On command , The master server will find that the current offset of the slave server is less than its own offset , The primary server then submits the copy offset from the secondary server , Find the missing data from the server in the replication buffer , And send these data to the slave server .