database engine

MyISAM and InnoDB

Data is stored in different ways , A table should store the table structure , Table data , Table index .

myisam

myisam A watch has proxies_priv.frm .myd .myi, His data and index are stored separately ,

innodb

In addition to storing table structures , Its data and index are stored in a file （server_cost.ibd）.frm. This is also innodb In the case of a storage engine , Even if you don't add a primary key to it , It will also automatically generate a primary key for you . and myisam Add primary key , Just to give you , Because the data and index are stored separately . Data belongs to data , The index belongs to the index .

myisam and innodb The difference between

MyISAM Unsupported transaction 、 Foreign keys are also not supported , The index adopts non clustered index , The advantage is the speed of access , There is no requirement for transaction integrity , With SELECT、INSERT Basically, the main application can use this storage engine to create tables .MyISAM The table is stored on disk as 3 File , The file name is the same as the table name , The extensions are ：

.frm（ Storage table definition ）
.MYD（MYData, Store the data ）
.MYI （MYIndex, Storage index ）

InnoDB The storage engine provides with commit 、 Transaction security of rollback and crash recovery capability , Support auto grow Columns , Foreign key and other functions , The index adopts clustered index , The index and data are stored in the same file , therefore InnoDB Your table has two files on disk , The file name is the same as the table name , The extensions are ：

.frm（ Definition of storage table ）
.ibd（ Store data and index ）
 Why is it InnoDB, You create a table , No primary key added , It automatically adds a primary key to you （ An integer column ） Well ？ Because data and index are stored together .

MEMORY The storage engine uses what is in memory to create tables . Every MEMORY Table only corresponds to one disk file , The format is .frm（ Table structure definition ）.MEMORY Type of table access is very fast , Because its data is in memory , And by default HASH Indexes （ Not suitable for range query ）, But once the service is shut down , The data in the table will be lost .

Differences between storage engines

a key ： Indexes , Locking mechanism , Business

Locking mechanism ： Indicates that when the database is accessed by concurrent requests , When multiple transactions operate , Granularity of concurrent operations .
B- Tree index and Hashi index ： Mainly to accelerate SQL Query speed of .
Foreign keys ： The fields of the child table depend on the primary key of the parent table , Set the dependency between the two tables .
Business ： Multiple SQL sentence , Ensure that they perform atomic operations together , Or success , Or failure , You can't succeed only partially , Failure requires rollback of the transaction .
Index cache and data cache ： and MySQL Server Query cache related , Before modifying the data and index , Repeated queries can be performed without disk I/O（ Improve the performance of the database , The purpose is to reduce disk I/O Operation to improve database access efficiency ）, Just read the cache of the last query in memory .