Master-slave replication and its principle

Redis The replication function of is to support data synchronization among multiple databases . The main database can be read and write , When the data in the master database changes, it will automatically synchronize the data to the slave database . The slave database is generally read-only , It will receive data synchronized from the primary database .

1. When starting a slave node , It will send one PSYNC Command to master ;

2. If the slave node is connected to the master node for the first time , Then a full copy will be triggered . At this point, the master node will start a background thread , Start making a copy of RDB Snapshot file ;

3. It will also be from the client side client All newly received write commands are cached in memory .RDB After file generation , The master node will RDB The file is sent to the slave node , The slave node will first RDB File write to local disk , Then load it from the local disk into memory ;

4. Then the master node sends the write command cached in memory to the slave node , Synchronize this data from the node ;

5. If the network between the slave node and the master node fails , The connection is broken , Will automatically reconnect , After connection, the master node will only synchronize some missing data to the slave node .