Mysql database: read write separation

One 、 The principle of separation of reading and writing ：

1、 Realization principle ：

The separation of reading and writing solves , data Library write operations , Affect the efficiency of the query , Suitable for scenarios where reading is far greater than writing . The implementation of read-write separation is based on master-slave replication , The master database uses master-slave replication to synchronize the changes of its own data to the slave database cluster , Then the master database is responsible for handling write operations （ Of course, you can also perform read operations ）, From the database is responsible for processing read operations , Can't write . And according to the pressure , Deploy multiple slave databases to improve the speed of read operations , Reduce the pressure on the primary database , Improve the overall performance of the system .

2、 The reason why read-write separation improves performance ：

（1） Add physical server , Load sharing ;

If we have 1 Lord 3 from , Suppose now 1 In minutes 10 The article writing ,150 Read . that ,1 Lord 3 From is equal to a total of 40 The article writing , And the total number of reads doesn't change , So on average, each server undertakes 10 Write and 50 Read （ The main library does not undertake the read operation ）. therefore , Although the writing has not changed , But the read is greatly spread , Improved system performance . in addition , When the read is allocated , And indirectly improve the write performance . therefore , Overall performance improved , That is, the machine and bandwidth are exchanged for performance .

（2） The master and the slave are only responsible for their own writing and reading , A great deal of relief X Lock and S Lock contention ;

（3） Configurable from library MyISAM engine , Improve query performance and save system overhead ;

（4） Another major function of master-slave replication is to increase redundancy , Improve availability , When a database server goes down, it can restore service as fast as possible by adjusting another slave database .

3、Mysql The implementation of reading, writing and writing ：

（1） Based on the internal implementation of program code ：

In the code according to select 、insert Route classification , This kind of method is also the most widely used in the current production environment . The advantage is better performance , Because the program is implemented in code , There's no need to add extra hardware , The disadvantage is that it needs developers to implement , Operation and maintenance personnel have no way to start .

（2） Based on the intermediate agent layer ：

The agent is generally between the application server and the database server , After receiving the request from the application server, the proxy database server forwards it to the back-end database according to the judgment , There are the following representative agent layers .

①mysql_proxy.mysql_proxy yes Mysql An open source project of , Through its own lua The script goes on sql Judge . ②Atlas. By qihoo 360, Web Platform Department infrastructure team development and maintenance based on MySQL Data middle tier project of the protocol . It's in mysql-proxy 0.8.2 Based on version , It's optimized , Added some new features .360 For internal use Atlas Running mysql Business , It carries billions of read and write requests every day . Support transactions and stored procedures . ③Amoeba. It is used by Chen Siru, an employee of Alibaba group java Language development , Alibaba group puts its users in the production environment , But it doesn't support things and stored procedures .

After the above simple comparison , Not all applications can implement read / write separation in program code , Like some big ones java application , If the separation of reading and writing is implemented in the program code, the code will be greatly changed , therefore , Applications like this generally consider using a proxy layer to implement .

Two 、 The construction of separation of reading and writing ：

The steps for setting up read / write separation , You can read these two blogs ：

https://blog.csdn.net/starlh35/article/details/78735510

https://blog.csdn.net/justdb/article/details/17331569

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