redis learns master-slave replication Master/slave

What is

Jargon: This is what we call master-slave replication. After the host data is updated, it is configured according to the configuration. and strategy, automatically synchronized to the master/slaver mechanism of the standby machine. The Master is mainly for writing, and the Slave is mainly for reading.

What can be done

Reading and writing separation
Disaster recovery

Recommended (free):redis

##How to play

• Configure slave (library) but not master (library)

• Slave library configuration command: slaveof master library IP master library port
• Every time you disconnect from the master, you need to reconnect, unless you configure it in redis.conf File (specific location: redis.conf search
# REPLICATION
#)
  • info replication
• Modify configuration file details operation
  • Copy multiple redis.conf files, press 'redis[ port].conf'Rename
  • Turn on daemonize yes
  • pid file name
  • Specify port
  • Log file name

  • dump.rdb name

replication English [ˌreplɪ'keɪʃ(ə)n] American [ˌreplɪ'keɪʃ(ə)n] n.

(painting, etc.) copy; copy; repeat (experiment); (especially the answer to the defense)

3 common tricks

One master and two slaves (one host, two slaves)

Init

Set the slave through slaveof 127.0.0.1 6379d
At this time, one master and two slaves are set up
Set k4 v4 in the master, and get in the two slaves k4 can be displayed.
1. If I set k1 and k2 before slave, can the slave machine check their values?
Yes, the slave machine can only play from beginning to end after receiving it. Play all of them on the host
2. At this time, set k6 v6 is set on the host. And set k6 v66 is also set on the two slaves. What will happen at this time? First come first served, the latter overrides. Can the slave and the host execute the same command?
The master writes as the master, and the slave reads as the master.
At this time, the slave cannot write and an exception is reported.
3. The host is dead? What are the chances? From the machine? Stay put?
Still slave, stay put. If you can’t take over, the leader is back, everything will be the same as before
4. Is the slave machine dead? Recover from inability to function?

If the slave machine dies, it will become the master when it recovers, because • Every time it is disconnected from the master, it needs to be reconnected, unless you configure it in redis.conf. If you want to keep up with the large army, just use the slaveof command. Start over from the beginning and play through the console from beginning to end.

passing on the fire

Core idea: decentralization
The previous Slave can be the Master of the next slave, and the Slave can also receive connections and connections from other slaves. Synchronous request, then the slave becomes the next master in the chain, which can effectively reduce the writing pressure of the master (slave of slaves is still a slave)
Midway change direction: the previous data will be cleared and the latest copy will be re-established
slaveof new main library IP new main library port

For example, 79 is the host of 80, and 80 is the host of 81. In 79, set k9 v9 can be queried between 80 and 81. Using info republication on the 80 host, it is a slave, but it is also connected to a slave.

Anti-customer-based

SLAVEOF no one
Stop the current database from synchronizing with other databases and turn it into the primary database

After the host hangs up, the two slaves The machine needs to choose a boss. At this time, use a command on 80, slave of no one, to make 80 the leader. For 81, if slaveof 80 is used, the 80-bit host will be recognized, and the data of 80 will be modified, and 81 can also be queried. If the original host 79 comes back, it will become an independent individual at this time.

Copying Principle

After the slave is successfully started and connected to the master, it will send a sync command
The master receives the command to start the background save process, and at the same time collects all received is used to modify the data set command. After the background process is executed, the master will transfer the entire data file to the slave to complete a complete synchronization
Full copy: After the slave service receives the database file data, it will save it and loaded into memory.
Incremental replication: Master continues to pass all new collected modification commands to slave in order to complete synchronization
However, as long as the master is reconnected, a full synchronization (full replication) will be automatically executed

For the first time It is a full copy, followed by an incremental copy.

Sentinel mode(sentinel)

A group of sentinels can monitor multiple masters at the same time (patrol sentinel)

What is it

An automatic version that is mainly anti-customer. It can monitor whether the host fails in the background. If it fails, it will automatically switch from the slave database to the main database based on the number of votes.

How to play (usage steps)

###

1. Adjust the structure, 6379 brings 6380 and 6381
2. Create a new sentinel.conf file, the name must not be wrong
3. Configure the sentinel, fill in the content
1.sentinel monitor The name of the monitored database (Choose your own name) 127.0.0.1 6379 1
ˆ ˆ 2. The last number 1 above means that after the host hangs up, the salve will vote to see who will take over as the host. The person who gets the number of votes will become the host (PS. It is different from the description on the official website. , there are official documents below)
4. Start Sentinel
1. redis-sentinel /sentinel.conf (the above directories are configured according to their actual conditions, and the directories may be different)
5. Normal master-slave demonstration
6. The original master is down
7. Vote for a new one
8. Restart the master and slave and continue working, check info replication

Question: If the previously hung master is restarted, Will there be a conflict between the two masters?
Answer: No, the original master becomes a slave

Disadvantages of replication

Replication delay

Because all write operations are It is operated on the Master first, and then synchronized to the slave, so 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 worse. serious.

More related free learning recommendations: redis tutorial

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