Advanced MySQL - storage engine

Catalog

Storage engine

InnoDB

MyISAM

Memory

choice

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In the last article, we learned MySQL Basics —— Business , This article is for learning MySQL Advanced —— Storage engine .

Storage engine

The storage engine is to store data 、 Index 、 to update / Query data and other technologies . Its table based , Not library based , So the storage engine is also called a table type .

While building the watch , If you do not specify a storage engine , Will use the default storage engine InnoDB, Execute the following code to view the previous table creation statement ：

use mytest;
show create table account;

As shown in the figure below ：

You can see , The storage engine of this data table is InnoDB.

While building the watch , You can specify the storage engine , The syntax is as follows ：

create table  Table name (
     Field 1  Field 1 type  [COMMENT  Field 1 notes ],
    ....
     Field n  Field n type  [COMMENT  Field n notes ],
)ENGINE = INNODB [COMMENT  Table annotation ];

Be careful ： Before specifying the storage engine , You need to query the storage engines supported by the current database , The code is as follows ：

show engines;

As shown in the figure below ：

InnoDB

InnoDB It is a general storage engine with high reliability and high performance , stay MySQL5.5 after ,InnoDB By default MySQL Storage engine .

Its main features are ：

• DML Operation follows ACID Model , Support transactions ;

• Row-level locks , Improve concurrent access performance ;

• Support foreign keys FOREIGN KEY constraint , Ensure the integrity and correctness of data ;

The suffix of the stored disk file is .ibd,InnoDB Each table of the engine will correspond to such a tablespace file , The table structure that stores the table （frm、sdi）、 Data and index .

Parameters have innodb_file_per_table, This parameter determines whether a table corresponds to a tablespace file or multiple tables share a tablespace file .

Check the parameter code as follows ：

show variables like 'innodb_file_per_table';

As shown in the figure below ：

You can see innodb_file_per_table The value of is ON, This means that a table corresponds to a tablespace file .

InnoDB The logical storage structure is as follows ：

among ：TableSpece Table space 、Segment paragraph 、Extent District ( Fixed size 1M)、Page page ( Fixed size 16k)、Row That's ok .

MyISAM

MyISAM yes MySQL Early default storage engine .

Its main characteristics are ：

• Unsupported transaction , Foreign key not supported ;

• Support table lock , Row locks are not supported ;

• Fast access .

stay MyISAM The disk space file suffixes involved are ：

• .MYD： Store table data ;

• .MYI： Storage index ;

• .sdi： Store information about the table structure .

Memory

Memory The table data of the engine is stored in memory , Due to hardware problems 、 Or the impact of power failure , These tables can only be used as temporary tables or caches .

Its main features are ：

• Memory storage , Fast access ;

• Support hash Indexes .

Its file suffix is sdi, This file stores table structure information .

choice

Before selecting a storage engine , We first compare the characteristics of these three storage engines , The following table ：

characteristic	InnoDB	MyISAM	Memory
Storage limits	64TB	Yes	Yes
Transaction security	Support	I won't support it	I won't support it
Locking mechanism	Row lock	Table locks	Table locks
B+tree Indexes	Support	Support	Support
Hash Indexes	I won't support it	I won't support it	Support
Full-text index	5.6 Support for	Support	I won't support it
Space use	high	low	N/A
Memory usage	high	low	secondary
Batch insertion speed	low	high	high
Support foreign keys	Support	I won't support it	I won't support it

There is no good or bad storage engine , We only need to select the appropriate storage engine according to the characteristics of the system , For complex systems , You can choose a variety of storage engines to combine according to the actual situation .

• InnoDB： yes MySQL Default storage engine , Support transactions 、 Foreign keys . When applications have high requirements for transaction integrity , Data consistency is required under concurrent conditions , Data operations in addition to inserts and queries , It also contains a lot of updates 、 Delete operation , that InnoDB The storage engine is a better choice .

• MyISAM： When the system is based on read operation and insert operation , There are very few update and delete operations , And the integrity of the transaction 、 Concurrency requirements are not very high , So choose MyISAM engine .

• Memory： Keep all data in memory , Fast access , Usually used for temporary tables and caches .Memory The limitation of table size is the limitation of table size , Too large tables cannot be cached in memory , The security of data cannot be guaranteed .

Okay ,MySQL Advanced —— That's what the storage engine learned , Next article study MySQL Advanced —— Indexes ( Structure and classification ).