MySQL storage system

One 、 Storage engine

MySQL The data in is stored in files with various technologies , Each technology uses a different storage mechanism 、 Indexing techniques 、 Lock levels and ultimately provide different functions and capabilities , These different technologies and supporting functions are in MySQL It's called storage engine in , The storage engine is MyISAM、InnoDB MySQL Components in the database , Responsible for executing the actual data l/0 operation MySQL In the system , The storage engine is on top of the file system , The data is transferred to the storage engine before it is saved to the data file , Then, it is stored according to the storage format of each storage engine .

Two 、MyISAM And Innodb

2.1MyISAM

MyISAM Table supported 3 Different storage formats

static state （ Fixed length ） surface ：
Static tables are the default storage format . Fields in static tables are immutable , So every record is a fixed length , The advantage of this storage method is that the storage is very fast , Easy to cache , It's easy to recover in case of failure ; The disadvantage is that it usually takes up more space than a dynamic table .

Dynamic table ：
Dynamic tables contain variable fields , Records are not fixed length , The advantage of this storage is that it takes up less space , But frequent updates 、 Deleting records will cause fragmentation , It needs to be carried out on a regular basis OPTIMIZE TABLE Sentence or myisamchk -r Command to improve performance , And it's relatively difficult to recover in case of failure .

Compression meter ：
The compressed table consists of myisamchk Tool creation , Take up a very small space , Because each record is compressed separately , So there's only a very small cost of access .

MyISAM Production scenarios used

MyISAM Advantages and disadvantages
MyISAM It's table level locking , Reading or writing cannot be done at the same time
The advantage is ： When executed separately , Fast 、 Relatively few resources are occupied （ relative ）

2.2Innodb

Innodb characteristic ：
1. Support things , Support 4 Isolation level of things
2.MySQL from 5.5.5 Version start , The default storage engine is Innodb,5.5 It used to be myisam（isam） Default
3. Read / write blocking is related to the isolation level of things
4. It can cache index and data very efficiently
5. Tables and primary keys are stored in clusters
6. Support partition 、 Table space , similar oracle database （5.5----》5.6 and 5.7 Third generation database 8.0 Later version ）
7. Support for foreign key constraints ,5.5 Full text indexing is not supported before ,5.5 Full text index is supported after
8. The requirement for hardware resources is relatively high
9. Row level locking , But full table scanning will still be table level locking

2.3MyISAM And Innodb difference

MyISAM Do not support things , Foreign key constraints are not supported either , Full text indexing only , Data files and index files are kept separately ; Fast access , There is no requirement for transaction integrity , Suitable for inquiry 、 Insert the main application scenario

Innodb Support things , Support 4 Isolation level of things , Support the index , Support for foreign key constraints

3、 ... and 、 Control statement

3.1 Check out the storage engines supported by the system

show engines;

3.2 Look at the storage engine that the table uses

Method 1 ：

show table status from  Library name  where name=‘ Table name ’\G;

Method 2 ：
use Library name ;
show create table Table name ;

3.3 Modify the storage engine

Method 1 ：
use Library name ;
alter table Table name engine=MyISAM;

Method 2 ：

vim /etc/my.cnf
…
[mysqld]
…
default-storage-engine=INNODB

systemctl restart mysqld

This method only changes the configuration file and restarts mysql The newly created table is valid after service , The existing table will not be changed . Create a new table to view


Method 3 ：
adopt create table Specify the storage engine when creating the table
create table Table name （ Field 1 data type ,…）engine=Innodb;