Redis replication (Master/Slave)

What is it?

It is the Master / Slave mechanism that we often call Master-Slave replication. After the host data is updated, it is automatically synchronized to the standby machine according to the configuration and policy. The Master is mainly written and the Slave is mainly read

What can I do?

Read write separation
Disaster recovery

How do you play?

With slave (Library) but not master (Library)

Configuration from library

#Configure slave Library

slaveof Main library ip Main library port

#View master-slave information

info replication

Every time you disconnect from the master, you need to reconnect unless you configure redis Conf file

Common master-slave mode

One master and two servants

Meaning: one Master and two Slave

View master-slave information through replication info

# Replication











# Replication




















be careful:

  1. The first entry point of slave1 and slave2 is full replication, followed by incremental replication
  2. The host can write, but the slave cannot write, and the slave can only read
  3. After the host shuts down, the slave is in standby mode. After the host returns, the new records of the host can be copied smoothly
  4. After the slave is shut down, it needs to be reconnected every time it is disconnected from the master, unless you configure redis Conf file
  5. The data copied from the local machine will be persisted by the local machine. Even if the shutdown is disconnected, there will still be data.
  6. Reconnecting or changing the master will clear the previous data and re-establish and copy the latest data

From generation to generation

Meaning: the previous slave can be the master of the next slave. The slave can also receive connection and synchronization requests from other slaves. Then the slave acts as the next master in the chain, which can effectively reduce the write pressure of the master.

The precautions are similar to that of one master and two servants, but note that although slave is a relative master, it is still slave [view] (#zhu yi)

turn from a guest into a host

SLAVEOF no one

Make the current database stop synchronizing with other databases and convert to the primary database

sentinel mode

The anti guest based automatic version can monitor whether the Master library fails in the background. If it fails, the slave library will be automatically converted to the main library according to the number of votes. A set of sentinel can

Monitor multiple masters at the same time.

Use steps:

  1. Corresponding to in the Master Create sentinel.conf under the same directory as conf Conf file, the name must not be wrong;
  2. Configure sentry at sentinel Fill the contents in the conf file (multiple can be configured):
#Note: the last number 1 means that after the host hangs up, the slave votes to see who will take over as the host and become the host after winning the number of votes.
sentinel monitor Name of monitored database (self named) ip port 1
  1. Start sentinel mode (the path is configured according to your own needs):
redis-sentinel  /myredis/sentinel.conf

be careful:

  1. When the master hangs up, the next master will be elected by ballot. And only sentinel Votes can only be opened when conf is started
  2. When the original master is later, it unfortunately becomes a slave.

Replication principle

  1. After Slave is successfully started and connected to the master, it will send a sync command;
  2. After receiving the command, the master starts the save process and collects all the commands received to modify the dataset. After the background process is executed, the master will transfer the whole data file to the slave to complete a complete synchronization;
  3. Full copy: the slave service saves the database file data and loads it into memory;
  4. Incremental replication: the Master continues to transmit all new collected modification commands to the slave in turn to complete the synchronization;
  5. However, as long as the master is reconnected, a full synchronization (full replication) will be performed automatically.

Disadvantages of replication

Delay: since all write operations are performed on the Master and then synchronously updated to the Slave, there is a certain delay in synchronizing from the Master to the Slave machine. When the system is very busy, the delay problem will be more serious, and the increase in the number of Slave machines will also make this problem more serious.


slaveof main library ip main library portConfigure slave Library
info replicationView the master-slave replication of redis
slaveof no oneMake the current database stop synchronizing with other databases and convert to the primary database
sentinel monitor name of monitored database (self named) 6379 1Configure sentry and monitor master
redis-sentinel /myredis/sentinel.confStart redis in sentinel mode

Keywords: Redis

Added by Deviants on Sat, 19 Feb 2022 12:57:41 +0200