Detailed explanation of redis persistence, master-slave synchronization and sentinel under Linux

1.0 Redis persistence

Redis is an in-memory database. Once the server process exits, the database data will be lost. To solve this problem, Redis provides two persistence solutions to save the data in memory to disk to avoid data loss.

1|1RDB persistence

Redis provides the RDB persistence function, which generates a point-in-time snapshot of the data set within a specified time interval. This function can save the state of Redis in memory to the hard disk. The RDB file generated by RDB persistence is a compressed binary file. This file is saved on the hard disk. Redis can restore the database state at that time through this file.

It can be performed manually.

It can also be configured in redis.conf and executed periodically.

Advantages: fast speed, suitable for backup, master-slave replication is based on RDB persistence function

rdb triggers rdb by using the save command in redis

rdb configuration parameters:

port 6379 
daemonize yes 
pidfile /data/6379/redis.pid
loglevel notice 
logfile "/data/6379/redis.log"
dir /data/6379 
protected-mode yes 
dbfilename dbmp.rdb
save 900 1
save 300 10 
save 60 10000

Every 900 seconds, there is an operation that is persisted

save 900 seconds 1 modification operation

save 300 seconds 10 operations

save 60 seconds 10000 operations

2. Trigger rdb persistence, or manually save command to generate dump.rdb persistence file

3. Restart redis, data is no longer lost

4. RDB data files are binary files and cannot be read manually.

1|2 Redis persistence AOF

AOF (append-only log file)

Record all change operation commands executed by the server (such as set del, etc.), and restore the data set by re-executing these commands when the server starts

All commands in the AOF file are saved in the format of the redis protocol, and new commands are appended to the end of the file.

Advantages: The maximum program guarantees that data will not be lost

Disadvantage: The log record is very large

Configuration

1. In the configuration file, add the aof parameter

Add parameters in redis-6379.conf to enable the aof function

appendonly yes
appendfsync everysec

2. Restart the redis database and load the aof function

3. Check whether the redis data directory /data/6379/ generates an aof file

[root@web02 6379]# ls
appendonly.aof dbmp.rdb redis.log

4. Log in to redis-cli, write data, and monitor aof file information in real time

tail -f appendonly.aof

5. Set a new key, check the aof information, then close redis and check whether the data is persistent

redis-cli -a redhat shutdown
redis-server /etc/redis.conf
redis-cli -a redhat

Without restarting redis, switch rdb data to aof data

1. Configure redis to support rdb persistence

2. Start the redis client and temporarily switch to aof mode through the command

127.0.0.1:6379> CONFIG set appendonly yes
OK
127.0.0.1:6379> CONFIG SET save ""
OK

3. Check whether the data persistence mode is rdb or aof, check the appendonly.aof file, and check the data changes

tail -f appendonly.aof

4. At this time, aof has not yet taken effect permanently, write the parameters to the configuration file

Edit redis-6379.conf and add the following parameters

appendonly yes
appendfsync everysec

2|0 Master-slave synchronization

Redis master-slave synchronization implementation

1. Prepare three redis databases, redis supports multiple instances

Three configuration files, only the ports are different

In the three configuration files, add the master-slave synchronization parameters

redis-6379.conf

port 6379 
daemonize yes 
pidfile /data/6379/redis.pid
loglevel notice 
logfile "/data/6379/redis.log"
dir /data/6379 
protected-mode yes 
dbfilename dbmp.rdb
save 900 1
save 300 10 
save 60 10000

redis-6380.conf

port 6380 
daemonize yes 
pidfile /data/6380/redis.pid
loglevel notice 
logfile "/data/6380/redis.log"
dir /data/6380 
protected-mode yes 
dbfilename dbmp.rdb
save 900 1
save 300 10 
save 60 10000
slaveof 127.0.0.1 6379

redis-6381.conf

port 6381 
daemonize yes 
pidfile /data/6381/redis.pid
loglevel notice 
logfile "/data/6381/redis.log"
dir /data/6381 
protected-mode yes 
dbfilename dbmp.rdb
save 900 1
save 300 10 
save 60 10000
slaveof 127.0.0.1 6379

2. Start three database instances and check the master-slave synchronization identity

redis-cli -p 6379 info replication 
redis-cli -p 6380 info replication 
redis-cli -p 6381 info replication

3: Make sure to check the information as follows and check whether it is synchronized

4. What if my main database crashes? ?

Solution:

1. Manually switch the master-slave identity and elect a new master database

1. Kill the 6379 main library
2. Disable your slave identity on 6380
slave of no one
3. Give new owner identity on 6381
salveof 127.0.0.1 6380
4. After the modification is completed, you must also modify the configuration file to make it permanent

2. Use Sentinel to automatically elect a new owner

2|1redis sentinel:

Sentinel function:

Sentinel detects whether the master-slave architecture is normal. If the master database fails, Sentinel will automatically modify redis.conf to add/delete the slaveof directive.

Redis Sentinel installation configuration:

1. Prepare three redis instances, one master and two slaves

See the redis master-slave configuration above for details

2. Prepare three database instances and start them

redis-server redis-6379.conf
redis-server redis-6380.conf
redis-server redis-6381.conf

3. Prepare three sentinels and start monitoring the master-slave architecture

Prepare three configuration files, sentinel files

redis-26379.conf

port 26379 
dir /var/redis/data/
logfile "26379.log"
sentinel monitor sbmaster 127.0.0.1 6379 2
Sentinel down-after-milliseconds QSmaster 30000
sentinel parallel-syncs sbmaster 1
sentinel failover-timeout sbmaster 180000
daemonize yes

redis-26380.conf

port 26380 
dir /var/redis/data/
logfile "26380.log"
sentinel monitor sbmaster 127.0.0.1 6379 2
Sentinel down-after-milliseconds QSmaster 30000
sentinel parallel-syncs sbmaster 1
sentinel failover-timeout sbmaster 180000
daemonize yes

redis-26381.conf

port 26381 
dir /var/redis/data/
logfile "26381.log"
sentinel monitor sbmaster 127.0.0.1 6379 2
Sentinel down-after-milliseconds sbmaster 30000
sentinel parallel-syncs sbmaster 1
sentinel failover-timeout sbmaster 180000
daemonize yes

4. Start three sentinel instances

redis-sentinel redis-26380.conf 
redis-sentinel redis-26379.conf 
redis-sentinel redis-26381.conf

Check whether the sentinel status is normal

Only if the following information is found and it is consistent with the following, it is normal

redis-cli -p 26379 info sentinel

# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=sbmaster,status=ok,address=127.0.0.1:6380,slaves=2,sentinels=3

5. Automatically switch between master and slave of Sentinel

1. Kill 6379 redis database

2. Check the identity information of 6380 and 6381 to see if they are automatically switched between master and slave (it will take 30 seconds to switch).

3. Manually start the database that has been hung up by 6379 to check whether it will be added to the master-slave cluster of information by Sentinel.

Notice! ! If you find that it is unsuccessful, you need to delete all Sentinel configuration files and start over. Note! ! If you find that it is unsuccessful, you need to delete all Sentinel configuration files and start over. Note! ! If it fails, you need to delete all Sentinel configuration files and start over.

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