MySQL storage engine

MySQL storage engine说明文档

MySQL中存储engine决定了表的类型(Storage engines are MySQL components that handle the SQL operations for different table types)，具体体现在以下特性的支持度：

存储机制、外键、索引技巧、锁定水平、事物支持（Transactions）、XA、Savepoints等。

根据不同的业务需求、数据量和访问读写特点，选择合适的engine，可以加速读、写性能，减少运维难度、提高访问难度(如MRG_MYISAM、MERGE)。

查询当前mysql支持的engine

mysql> SHOW VARIABLES LIKE "%version%";
+-------------------------+------------------------------+
| Variable_name           | Value                        |
+-------------------------+------------------------------+
| innodb_version          | 5.7.20                       |
| protocol_version        | 10                           |
| slave_type_conversions  |                              |
| tls_version             | TLSv1,TLSv1.1                |
| version                 | 5.7.20                       |
.....

mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+

不同engine的特性

以下摘自MySQL 8.0 官方文档

• Where can I obtain complete documentation for MySQL storage engines?
• Chapter 16 Alternative Storage Engines
• Chapter 15 The InnoDB Storage Engine
• Chapter 22 MySQL NDB Cluster 8.0

InnoDB: The default storage engine in MySQL 8.0.

• transaction-safe (ACID compliant) storage engine for MySQL that has commit,
• rollback
• crash-recovery capabilities to protect user data.
• row-level locking (without escalation to coarser granularity locks)
• Oracle-style consistent nonlocking reads increase multi-user concurrency and performance.
• InnoDB stores user data in clustered indexes to reduce I/O for common queries based on primary keys.
• To maintain data integrity, InnoDB also supports FOREIGN KEY referential-integrity constraints.

MyISAM: These tables have a small footprint.

• Table-level locking limits the performance in read/write workloads, so it is often used in read-only or read-mostly workloads in Web and data warehousing configurations.

Memory: Stores all data in RAM, for fast access in environments that require quick lookups of non-critical data. This engine was formerly known as the HEAP engine. Its use cases are decreasing; InnoDB with its buffer pool memory area provides a general-purpose and durable way to keep most or all data in memory, and NDBCLUSTER provides fast key-value lookups for huge distributed data sets.

CSV: Its tables are really text files with comma-separated values. CSV tables let you import or dump data in CSV format, to exchange data with scripts and applications that read and write that same format. Because CSV tables are not indexed, you typically keep the data in InnoDB tables during normal operation, and only use CSV tables during the import or export stage.

Archive: These compact, unindexed tables are intended for storing and retrieving large amounts of seldom-referenced historical, archived, or security audit information.

Blackhole: The Blackhole storage engine accepts but does not store data, similar to the Unix /dev/null device. Queries always return an empty set. These tables can be used in replication configurations where DML statements are sent to slave servers, but the master server does not keep its own copy of the data.

NDB (also known as NDBCLUSTER): This clustered database engine is particularly suited for applications that require the highest possible degree of uptime and availability.

Merge: Enables a MySQL DBA or developer to logically group a series of identical MyISAM tables and reference them as one object. Good for VLDB environments such as data warehousing.

Federated: Offers the ability to link separate MySQL servers to create one logical database from many physical servers. Very good for distributed or data mart environments.

Example: This engine serves as an example in the MySQL source code that illustrates how to begin writing new storage engines. It is primarily of interest to developers. The storage engine is a “stub” that does nothing. You can create tables with this engine, but no data can be stored in them or retrieved from them.