1、存储引擎
1.1、MySQL 体系结构
自上而下可以分为
- 连接层
- 接受客户端的连接，完成连接的处理、认证授权、安全方案和最大连接数等
- 服务层
- 绝大部分的核心功能都是在服务层完成的，比如SQL 接口（DDL、DML、视图、触发器、存储过程）、解析器、查询优化器和缓存等
- 存储引擎层
- 存储引擎控制着数据的存储和提取的方式，服务器通过 API 和存储引擎通信
- 注意：索引是在存储引擎层实现的，不同的存储引擎索引的结构是不同的
- InnoDB 是 MySQL 5.5 之后默认的存储引擎
- 存储层
- 真正存储数据的地方，除了数据还有各种日志
1.2、存储引擎简介
存储引擎是存储数据、建立索引、更新/查询数据等技术的实现方式。存储引擎是基于表的，而不是基于库的，所以存储引擎也可以被称为表类型。
1.2.1、在创建表时，指定存储引擎
CREATE TABLE xx (
)ENGINE=INNODB;1.2.2、查看当前数据库支持的存储引擎
SHOW ENGINGS;
1.3、存储引擎特点
1.3.1、InnoDB
1）介绍
InnoDB 是 MySQL 中一种兼顾高可靠性和高性能的通用存储引擎，MySQL 5.5 之后，InnoDB 是默认的 MySQL 存储引擎。
2）特点
- DML 操作（表数据的CRUD）遵循 ACID 模型，支持事务；
- 行级锁，提升高并发访问性能；
- 支持外键约束，保证数据的完整性和正确性；
3）文件
- xxx.ibd：xxx代表表名，每一个 InnoDB 的表都会对应这样一个表空间文件，存储该表的表结构（8.0 之后存储在 sdi 这个数据字典当中）、数据和索引；
- 参数：innodb_file_per_table（MySQL 8.0 中是 ON，也就是每张表都有一个 InnoDB 文件）
我们可以查看数据库表对应的 InnoDB 文件：
可以通过指令 "ibd2sdi student.ibd" 来查看这个二进制文件：
["ibd2sdi"
,
{
"type": 1,
"id": 713,
"object":
{
"mysqld_version_id": 80030,
"dd_version": 80023,
"sdi_version": 80019,
"dd_object_type": "Table",
"dd_object": {
"name": "student",
"mysql_version_id": 80030,
"created": 20240513090135,
"last_altered": 20240513090135,
"hidden": 1,
"options": "avg_row_length=0;encrypt_type=N;key_block_size=0;keys_disabled=0;pack_record=1;stats_auto_recalc=0;stats_sample_pages=0;",
"columns": [
{
"name": "id",
"type": 4,
"is_nullable": true,
"is_zerofill": false,
"is_unsigned": false,
"is_auto_increment": false,
"is_virtual": false,
"hidden": 1,
"ordinal_position": 1,
"char_length": 11,
"numeric_precision": 10,
"numeric_scale": 0,
"numeric_scale_null": false,
"datetime_precision": 0,
"datetime_precision_null": 1,
"has_no_default": false,
"default_value_null": true,
"srs_id_null": true,
"srs_id": 0,
"default_value": "",
"default_value_utf8_null": true,
"default_value_utf8": "",
"default_option": "",
"update_option": "",
"comment": "",
"generation_expression": "",
"generation_expression_utf8": "",
"options": "interval_count=0;",
"se_private_data": "physical_pos=3;table_id=1187;",
"engine_attribute": "",
"secondary_engine_attribute": "",
"column_key": 1,
"column_type_utf8": "int",
"elements": [],
"collation_id": 8,
"is_explicit_collation": false
},
{
"name": "name",
"type": 16,
"is_nullable": true,
"is_zerofill": false,
"is_unsigned": false,
"is_auto_increment": false,
"is_virtual": false,
"hidden": 1,
"ordinal_position": 2,
"char_length": 24,
"numeric_precision": 0,
"numeric_scale": 0,
"numeric_scale_null": true,
"datetime_precision": 0,
"datetime_precision_null": 1,
"has_no_default": false,
"default_value_null": true,
"srs_id_null": true,
"srs_id": 0,
"default_value": "",
"default_value_utf8_null": true,
"default_value_utf8": "",
"default_option": "",
"update_option": "",
"comment": "",
"generation_expression": "",
"generation_expression_utf8": "",
"options": "interval_count=0;",
"se_private_data": "physical_pos=4;table_id=1187;",
"engine_attribute": "",
"secondary_engine_attribute": "",
"column_key": 1,
"column_type_utf8": "varchar(6)",
"elements": [],
"collation_id": 255,
"is_explicit_collation": false
},
{
"name": "sex",
"type": 16,
"is_nullable": true,
"is_zerofill": false,
"is_unsigned": false,
"is_auto_increment": false,
"is_virtual": false,
"hidden": 1,
"ordinal_position": 3,
"char_length": 4,
"numeric_precision": 0,
"numeric_scale": 0,
"numeric_scale_null": true,
"datetime_precision": 0,
"datetime_precision_null": 1,
"has_no_default": false,
"default_value_null": true,
"srs_id_null": true,
"srs_id": 0,
"default_value": "",
"default_value_utf8_null": true,
"default_value_utf8": "",
"default_option": "",
"update_option": "",
"comment": "",
"generation_expression": "",
"generation_expression_utf8": "",
"options": "interval_count=0;",
"se_private_data": "physical_pos=5;table_id=1187;",
"engine_attribute": "",
"secondary_engine_attribute": "",
"column_key": 1,
"column_type_utf8": "varchar(1)",
"elements": [],
"collation_id": 255,
"is_explicit_collation": false
},
{
"name": "age",
"type": 4,
"is_nullable": true,
"is_zerofill": false,
"is_unsigned": false,
"is_auto_increment": false,
"is_virtual": false,
"hidden": 1,
"ordinal_position": 4,
"char_length": 11,
"numeric_precision": 10,
"numeric_scale": 0,
"numeric_scale_null": false,
"datetime_precision": 0,
"datetime_precision_null": 1,
"has_no_default": false,
"default_value_null": true,
"srs_id_null": true,
"srs_id": 0,
"default_value": "",
"default_value_utf8_null": true,
"default_value_utf8": "",
"default_option": "",
"update_option": "",
"comment": "",
"generation_expression": "",
"generation_expression_utf8": "",
"options": "interval_count=0;",
"se_private_data": "default_null=1;physical_pos=6;table_id=1187;version_added=1;",
"engine_attribute": "",
"secondary_engine_attribute": "",
"column_key": 1,
"column_type_utf8": "int",
"elements": [],
"collation_id": 255,
"is_explicit_collation": false
},
{
"name": "DB_ROW_ID",
"type": 10,
"is_nullable": false,
"is_zerofill": false,
"is_unsigned": false,
"is_auto_increment": false,
"is_virtual": false,
"hidden": 2,
"ordinal_position": 5,
"char_length": 6,
"numeric_precision": 0,
"numeric_scale": 0,
"numeric_scale_null": true,
"datetime_precision": 0,
"datetime_precision_null": 1,
"has_no_default": false,
"default_value_null": true,
"srs_id_null": true,
"srs_id": 0,
"default_value": "",
"default_value_utf8_null": true,
"default_value_utf8": "",
"default_option": "",
"update_option": "",
"comment": "",
"generation_expression": "",
"generation_expression_utf8": "",
"options": "",
"se_private_data": "physical_pos=0;table_id=1187;",
"engine_attribute": "",
"secondary_engine_attribute": "",
"column_key": 1,
"column_type_utf8": "",
"elements": [],
"collation_id": 63,
"is_explicit_collation": false
},
{
"name": "DB_TRX_ID",
"type": 10,
"is_nullable": false,
"is_zerofill": false,
"is_unsigned": false,
"is_auto_increment": false,
"is_virtual": false,
"hidden": 2,
"ordinal_position": 6,
"char_length": 6,
"numeric_precision": 0,
"numeric_scale": 0,
"numeric_scale_null": true,
"datetime_precision": 0,
"datetime_precision_null": 1,
"has_no_default": false,
"default_value_null": true,
"srs_id_null": true,
"srs_id": 0,
"default_value": "",
"default_value_utf8_null": true,
"default_value_utf8": "",
"default_option": "",
"update_option": "",
"comment": "",
"generation_expression": "",
"generation_expression_utf8": "",
"options": "",
"se_private_data": "physical_pos=1;table_id=1187;",
"engine_attribute": "",
"secondary_engine_attribute": "",
"column_key": 1,
"column_type_utf8": "",
"elements": [],
"collation_id": 63,
"is_explicit_collation": false
},
{
"name": "DB_ROLL_PTR",
"type": 9,
"is_nullable": false,
"is_zerofill": false,
"is_unsigned": false,
"is_auto_increment": false,
"is_virtual": false,
"hidden": 2,
"ordinal_position": 7,
"char_length": 7,
"numeric_precision": 0,
"numeric_scale": 0,
"numeric_scale_null": true,
"datetime_precision": 0,
"datetime_precision_null": 1,
"has_no_default": false,
"default_value_null": true,
"srs_id_null": true,
"srs_id": 0,
"default_value": "",
"default_value_utf8_null": true,
"default_value_utf8": "",
"default_option": "",
"update_option": "",
"comment": "",
"generation_expression": "",
"generation_expression_utf8": "",
"options": "",
"se_private_data": "physical_pos=2;table_id=1187;",
"engine_attribute": "",
"secondary_engine_attribute": "",
"column_key": 1,
"column_type_utf8": "",
"elements": [],
"collation_id": 63,
"is_explicit_collation": false
}
],
"schema_ref": "test",
"se_private_id": 1187,
"engine": "InnoDB",
"last_checked_for_upgrade_version_id": 0,
"comment": "",
"se_private_data": "",
"engine_attribute": "",
"secondary_engine_attribute": "",
"row_format": 2,
"partition_type": 0,
"partition_expression": "",
"partition_expression_utf8": "",
"default_partitioning": 0,
"subpartition_type": 0,
"subpartition_expression": "",
"subpartition_expression_utf8": "",
"default_subpartitioning": 0,
"indexes": [
{
"name": "PRIMARY",
"hidden": true,
"is_generated": false,
"ordinal_position": 1,
"comment": "",
"options": "",
"se_private_data": "id=344;root=4;space_id=126;table_id=1187;trx_id=38435;",
"type": 2,
"algorithm": 2,
"is_algorithm_explicit": false,
"is_visible": true,
"engine": "InnoDB",
"engine_attribute": "",
"secondary_engine_attribute": "",
"elements": [
{
"ordinal_position": 1,
"length": 4294967295,
"order": 2,
"hidden": true,
"column_opx": 4
},
{
"ordinal_position": 2,
"length": 4294967295,
"order": 2,
"hidden": true,
"column_opx": 5
},
{
"ordinal_position": 3,
"length": 4294967295,
"order": 2,
"hidden": true,
"column_opx": 6
},
{
"ordinal_position": 4,
"length": 4294967295,
"order": 2,
"hidden": true,
"column_opx": 0
},
{
"ordinal_position": 5,
"length": 4294967295,
"order": 2,
"hidden": true,
"column_opx": 1
},
{
"ordinal_position": 6,
"length": 4294967295,
"order": 2,
"hidden": true,
"column_opx": 2
},
{
"ordinal_position": 7,
"length": 4294967295,
"order": 2,
"hidden": true,
"column_opx": 3
}
],
"tablespace_ref": "test/student"
}
],
"foreign_keys": [],
"check_constraints": [],
"partitions": [],
"collation_id": 255
}
}
}
,
{
"type": 2,
"id": 131,
"object":
{
"mysqld_version_id": 80030,
"dd_version": 80023,
"sdi_version": 80019,
"dd_object_type": "Tablespace",
"dd_object": {
"name": "test/student",
"comment": "",
"options": "autoextend_size=0;encryption=N;",
"se_private_data": "flags=16417;id=126;server_version=80030;space_version=1;state=normal;",
"engine": "InnoDB",
"engine_attribute": "",
"files": [
{
"ordinal_position": 1,
"filename": ".\\test\\student.ibd",
"se_private_data": "id=126;"
}
]
}
}
}
]可以看到，它是 json 格式存储的，里面描述了这张表的字段、索引等各种信息。
4）逻辑存储结构
一个 ibd 文件就代表一个表空间
在 InnoDB 的逻辑存储结构中，Page 是磁盘操作的最小单位，一个区就是 1 MB，一个 Page 16KB，一个区可以存放 64 页。
1.3.2、MyISAM
1）介绍
MyISAM 是 MySQL 早期默认的存储引擎；
2）特点
- 不支持事务和外键；
- 支持表锁，不支持行锁；
- 访问速度快；
3）文件
- xxx.sdi：存储表结构信息
- xxx.MYD：存储数据
- xxx.MYI：存储索引
1.3.3、Memory
1）介绍
Memory 引擎的表数据存储在内存，所以这些表只能做临时表
2）特点
- 数据存储在内存，访问速度快
- hash 索引（默认）
3）文件
- xxx.sdi：存储表结构信息
1.3.4、总结
