Alignment HR_ MySQL storage engine, so it is

MySQL Advanced storage engine

Thank you very much " a brand of instant noodles "

1. first impressions are strongest

1.1 see MySQL Supported storage engines

SHOW ENGINES;

1.2 View of the default storage engine

# Method 1 
SHOW VARIABLES LIKE '%storage_engine%'

# Method 2 
SELECT @@SESSION.default_storage_engine;

1.3 Modify the default storage engine

# Method 1   Modify the system variable of the current session layer 
SET SESSION default_storage_engine = ' Storage engine ';

# Method 2   modify my.cnf The configuration file 
[mysqld]
default_storage_engine =  Storage engine ;

1.4 Specify the corresponding storage engine when creating the table

CREATE TABLE IF NOT EXISTS table_name (
	field_name data_type constraint,
    field_name data_type constraint,
    field_name data_type constraint
)engine = ' Storage engine ';

# If no storage engine is specified, the default storage engine is used Innodb

1.5 Modify the storage engine of the table

ALTER TABLE table_name engine = ' Storage engine ';

2. The introduction of storage engine

2.1 What is a storage engine

• The storage engine can be understood as a table type , That is, it seems that variables have corresponding data types , Tables also have corresponding types , It's the storage engine
• The storage engine determines how the table handles the data
• Be careful : The above two points are based on the fact that the storage engine determines the underlying index , Indexes correspond to different data structures

2.2Innodb Storage engine

• since MySQL5.5 after , The default storage engine is changed to Innodb, The previous default storage engines were MYISAM

  • No special circumstances , priority of use Innodb

• Innodb It's transactional , namely Innodb Support Rollback operation \

• Innodb It supports foreign key constraints

• common DML operation Such as SELECT UPDATE DELETE INSERT Should be used Innodb This storage engine

  • The main reasons for using this engine are MySQL Yes Innodb Optimized , More efficient
  • Underlying index MYISAM The corresponding non clustered index is theoretically more efficient Later on

• File directory

  • MySQL8.0
    • .ibd Table structure + Table data / Indexes ( Data is index , Index and data )
  • MySQL5.7
    • .opt database information
    • .frm: Table structure
    • .ibd: Table data / Indexes ( Data is index , Index is data )

2.3MYISAM Storage engine

• MYISAM Neither foreign key constraints nor transactions are supported
• MYISAM The biggest advantage is high query efficiency , It is also related to non clustered indexes
• File directory
  • MYSQL8.0
    • .MYD Store the data
    • .MYI Storage index
    • .sdi Table structure
  • MySQL5.7
    • .MYD Store the data
    • .MYI Storage index
    • .frm Table structure
    • .opt database information

2.4Innodb and MYISAM The difference between

Contrast item	MYISAM	InnoDb	explain
Foreign keys	I won't support it	Support
Business	I won't support it	Support
Row table lock	Table lock	Row-level locks	With Java For example , Be similar to synchronized The role of
cache	Cache index only , Don't cache data	Data and indexes are cached together	The reason is also related to whether the underlying is a clustered index , therefore ,InnoDb Higher cache requirements , To a certain extent i Choose which performance
Use the self-contained system table	Y	N
concerns	Save resources , Less consumption , Simple business	High concurrency , Business , Large amount of data
Default installation	Y	Y
By default	N	Y

2.5Archive Storage engine

• Archive It's called archiving , As the name suggests, its main function is to Archive the data , Data archiving
• because Archive The main function of is to archive , It supports DML operation Only SELECT & INSERT operation
  • among SELECT It's less efficient ,INSERT Very efficient

2.6Blackhole Storage engine

• stay Blackhole In the storage engine ,INSERT Operation not allowed ,SELECT The operation returns NULL
• therefore DML The core query and insert operations are invalid , This storage engine makes no sense

2.7CSV Storage engine

• CSV The biggest highlight of the storage engine is that it generates the following file directories
  • .CSV This file stores the data in the table , This file can be opened by other software , Such as Excel etc.
  • .CSM This file stores the status of the table
• CSV The most important function is to visualize the tables in the database , You can open it directly with other software , Be similar to JSON and XML

2.8Memory Storage engine

• Memory The biggest highlight of the storage engine is , Other storage engines store data on disk , and Memory The data is stored in memory
  • so memory In the file directory structure under , stay mysq5.7 Only .frm file , stay mysql8.0 There are no documents
• Because the data is stored in memory
  1. The response speed is very fast , Query efficiency is very high The bottom layer is the hash index , The time complexity of the query element is O(1), Even if it's B+Tree The corresponding cluster index is also O(log2N)
  2. Data is easy to lose , Short life cycle once mysql Service terminated , Or restart , The corresponding memory will disappear
• Memory Data files and index files are stored separately , Because the bottom layer is not Cluster index
• Memory The size of is limited , Mainly depends on max_rows and max_heap_table_size
  • max_rows When creating a table, you can specify
  • max_heap_table_size The default is 16mb, It can be increased as needed
  • The above two are similar to the relationship between independent variables and dependent variables
• Memory Usage scenarios of
  • The data is provisional , And must be used immediately , And it doesn't matter if the data is discarded
  • The amount of data is relatively small , And be used frequently
    • In fact, this sentence is not accurate , For the bottom layer Hash index It is not suitable to do some Sort , Find range values The operation of

Similar to the relationship between independent variable and dependent variable

• Memory Usage scenarios of
  • The data is provisional , And must be used immediately , And it doesn't matter if the data is discarded
  • The amount of data is relatively small , And be used frequently
    • In fact, this sentence is not accurate , For the bottom layer Hash index It is not suitable to do some Sort , Find range values The operation of