MySQL optimization

You did MySQL Optimization of ？
First of all, there are some places that can be optimized SQL Statement and index optimization 、 Application optimization and MySQL Server Optimize , Let's go into details .

One 、SQL Statement and index optimization

When the amount of data is large , if SQL The statement is not written properly , It can lead to SQL The execution efficiency of is low , We need to wait a long time to get the results , We will use explain To analyze what SQL Caused by statement , But there are thousands of real enterprise projects SQL, We can't start from scratch, one by one explain To analyze , We should use slow query logs to analyze .

explain Analyze possible problems ：

• Too much data , It can be done by limit Pagination
• No index is used
• Using multi column index does not use the first column , The index is not used
• The size table setting of joint query is unreasonable , The index is useless （ Small table is the whole table query , Index only for large tables ）
• Multi table query does not need in（ Generate intermediate tables ）, Replace the belt with an external connection in The process of subquery , Use index reasonably

Two 、 Application optimization

Besides optimization SQL And index , In the actual production environment , Due to the performance limitations of the database server itself , We must optimize the application of the upper layer , So that the pressure of the upper application accessing the database can be minimized

• Introduce database connection pool ; Prevent the client from repeatedly shaking hands three times to establish a connection , Four waves to close the connection , Consume network and server resources , We can introduce database connection pool , This is a common optimization method in high concurrency scenarios
  

• Introduce caching ; Used to store hotspot data , If the client's request comes , First in redis Check it out （redis It's a memory based database ）, If redis If you find it directly on the Internet, you don't go through MySQL database , If you don't find it, visit MySQL database , visit MySQL After completion , First, send the currently accessed data to redis Let's cache it , And then return the results to the user

introduce redis Cache words , If the interviewer asks redis, Maybe I will ask some questions next ： Cache data consistency problem , Cache penetration and cache avalanche , Publish subscribe （ Used by chat server ）,redis What else do you know about it ？

3、 ... and 、MySQL Server Optimize

about MySQL Server End optimization , Mainly refers to MySQL Server Profile loaded at startup （my.ini or my.cnf） Optimization of configuration items in , Let's take a look at the optimization parameters that we need to focus on in the configuration file .

1. adaptive hash index

If the frequency of using adaptive hash index is not high , Maintaining an adaptive hash index itself requires a lot of performance , adopt show engine innodb status\G The command looks at adaptive hash index searches less frequently than secondary index tree searches , If the frequency of using adaptive hash index is not high , You can turn off adaptive hash indexing through parameter configuration , You can go through the variables innodb_adaptive_hash_index Turn off adaptive hash indexing .

2. redo log

You can set InnoDB log buffer size （redo log Cache size ）,Innodb_buffer_pool_size（ Cache size ）, To reduce disk I/O frequency , Because the cache is large , Working in the buffer for a long time ,redo log The efficiency is higher .
my.cnf Path to file /etc/my.cnf, The configuration file is as follows ：

3. MySQL The query cache

MySQL The query cache is the last time select Record the query results and put them in the cache , The next time you query the same content , Just take it out of the cache , You don't have to do it again SQL Inquire about （ Divide a space in memory for cache ）

Query caching is suitable for tables that are not updated frequently , Frequently queried tables , Because when two select Appear in the middle of query insert,update,delete At the time of statement , The query cache will be emptied , Too many queries add and delete cached data , It will affect MySQL Efficiency of execution , Maybe it's better to query from the disk every time （ A cache is a block of memory , Memory I/O Compare disk I/O Much faster ）

Can be in MySQL Through the following command , To view the query cache settings ：

If a table has more queries and less changes , Consider turning on the query cache

adopt show status command , You can see MySQL Query cache usage , as follows ：

Can pass set Command to set the above cache parameters to enable MySQL Query cache function , You can also find MySQL Configuration file for （windows yes my.ini,linux yes my.cnf）, modify query_cache_type Parameter is 1 That's all right. , And then restart MySQL Server You can use it , as follows ：

MySQL Query caching is better than using redis, This is a MySQL The query cache , We as MySQL For service users , Can't control MySQL Cache mode , If we introduce redis Words , Can pass redis Provided API Precisely control the data to be cached , And non cached data

4. MySQL Thread cache

It mainly refers to... In the configuration file thread_cache_size Configuration item .MySQL Server The network module adopts the classic select I/O Reuse + Thread pool model , The reason why thread pool is introduced , Mainly for the purpose of business execution , Not because of temporary creation and destruction of threads , Cause system performance degradation , Because the creation and destruction of threads is very performance consuming .

Thread pool is before business use , First create a fixed number of threads , Waiting for events to happen , When there is SQL Request arrival MySQL Server When , Take a thread from the thread pool to execute the process SQL Just ask , After execution , Don't destroy threads , Instead, return the thread to the thread pool , Wait for the processing of the next task （ The number of threads in the thread pool increases with requests , It can be added dynamically ）

End of configuration thread_cache_size, restart MySQL Server It will take effect after service

5. Number of concurrent connections and timeout

MySQL Server As a server , You can set the maximum number of connections and connection timeout of the client , If the number of database connections is large , The values of these two parameters need to be set larger .
In profile （my.ini or my.cnf） At the bottom , Add the configuration max_connections=2000, And then restart MySQL Server, Settings take effect .

MySQL Server For connections that haven't communicated for a long time , It closes the connection . Set timeout , When the set time is exceeded, disconnect without request , The unit is seconds , Add configuration... To the configuration file ：wait_timeout = 600