One 、 summary

stand-alone redis The problem is

Capacity is insufficient , a redis Insufficient capacity when writing data ？

Concurrency issues , a redis There is a concurrency problem when writing data ？

In master-slave mode , Host downtime or master-slave modification , Need to be in redis Revision in China ip The address is troublesome

redis3.0 The former is through host agent ,3.0 The non centralized cluster configuration is recommended

Two 、 build

Create a myredis Folder （ Here, you can simulate multiple servers by modifying multiple configuration file ports ） Copy redis.conf file 6 Share

The contents of each document are as follows （ Each file port is different ）

include /myredis/redis.conf
pidfile "/var/run/redis_6379.pid"
port 6379
dbfilename "dump6379.rdb"
cluster-enabled yes
cluster-config-file nodes-6379.conf
cluster-node-timeout 15000

start-up 6 individual redis see

Check the current directory file again , You can see that the corresponding node configuration file has been generated

Put six redis Compose a cluster

Get into redis Location

cd /opt/redis-6.2.1/src
redis-cli --cluster create --cluster-relicas 1 192.168.10:6379 192.168.10:6389 192.168.10:6380 192.168.10:6381 192.168.10:6390 192.168.10:6391

explain ：

• A cluster has at least three primary nodes
• relicas 1  It means to build a cluster in the simplest way That is, one master and one cluster just 3 Group
• The allocation principle tries to ensure that each master database runs on different servers ip Address , Each slave library and master library are not in one ip Address

Running effect

Connect to the cluster and see

redis-cli -c -p 6379
# Any port is ok 
cluster nodes

3、 ... and 、 slot

The above first 2 After clicking the synthesis, you can see the final output of the following sentence

All 16384 slots covered

One redis The cluster contains 16384 Slots , Every key in the database belongs to this 16384 One of the slots .

The cluster uses the formula CRC16(key)%16384 To calculate the key key Which slot does it belong to , among CRC16(key) Statements are used to evaluate keys key Of CRC16 Inspection and

Each node in the cluster is responsible for processing a portion of the slots , Let's take an example , If a cluster can have a master node , among ：

A Nodes are responsible for handling 0 No. to 5460 Slot number

B Nodes are responsible for handling 5461 to 10922 Slot number

C Nodes are responsible for handling 10923 to 16383 Slot number

Test insert a pair key-value, There are obvious slot assignments

But if you insert multiple pairs key-value Problems arise

The above problems can be solved by grouping , Use the following user grouping

Check the slot key Corresponding slot value

cluster keyslot k1

Count slots key The number of

cluster countkeysinslot 4837

View the value of the specified number in the slot

cluster getkeysinslot 449 10

Four 、 Cluster failover

1、 If you go offline through the master node ？ Whether the slave node can be automatically promoted to the master node ？15 Second timeout

Hang up 6379 You can see 6389 Become a host , When 6379 Recovery automatically becomes 6389 Slave

2、 A node in the cluster Both master and slave are down

If the master and slave of a certain slot hang up , and cluster-require-full-coverage by yes, Then the whole cluster will hang up , The master and slave of a slot in ancient China are all hung up , Two cluster-require-full-coverage by no, Then all the data in this slot cannot be used or stored

5、 ... and 、jedis Cluster development

redis Decentralization adopted . Even if the host is not connected , The cluster automatically switches host storage , Host write Read from machine , No matter which host writes data , Other hosts can read data