存储引擎(Storage Engine)是处理不同类型的表的SQL操作的MySQL部件，也被称为表类型。
MySQL支持多种的存储引擎，比如最新的MySQL 5.6就支持InnoDB、MyISAM、Memory、CSV、 Archive、Blackhole、Merge、Federated、Example等9种存储引擎；不同存储引擎的各自功能、性能和适用场景都各不相同。
5.5.5版本之前的MySQL是使用MyISAM作为默认的存储引擎的；而从5.5.5版本开始，MySQL使用InnoDB作为默认的存储引擎。
查看MySQL支持的存储引擎：
使用“show engines;”SQL语句可以查询当前MySQL支持的存储引擎，如下是在RHEL中的MySQL 5.1.61中的信息：
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mysql> show engines; +------------+---------+------------------------------------------------------------+--------------+------+------------+ | Engine | Support | Comment | Transactions | XA | Savepoints | +------------+---------+------------------------------------------------------------+--------------+------+------------+ | MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO | | CSV | YES | CSV storage engine | NO | NO | NO | | MyISAM | DEFAULT | Default engine as of MySQL 3.23 with great performance | NO | NO | NO | | InnoDB | YES | Supports transactions, row-level locking, and foreign keys | YES | YES | YES | | MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO | +------------+---------+------------------------------------------------------------+--------------+------+------------+ 5 rows in set (0.00 sec) |
其中Support字段为DEFAULT的引擎是默认的存储引擎。
查看数据库中各个表使用的存储引擎：
mysql> SHOW TABLE STATUS FROM my-db-name;
指定存储引擎（配置）：
1. 在mysql配置文件（/etc/my.conf）中指定默认引擎，如用“default-storage-engine=innodb”设置就指定了InnoDB为默认的存储引擎。
2. 在启动mysqld的命令行时添加“--default-storage-engine=innodb”或“--default-table-type=myisam”这样的参数（PS:对于RHEL系统中mysqld服务，可以修改/etc/init.d/mysqld文件中的 $exec 这一行).
3. 创建表时指定存储引擎的类型，如： CREATE TABLE mytable (id int, title char(20)) ENGINE=innodb
4. 改变一个表使用的存储引擎，SQL语句为：ALTER TABLE mytable ENGINE=MyISAM
不同存储引擎的区别：
InnoDB是支持事务的，具有ACID（A: atomicity. C: consistency. I:isolation.D: durability.原子性、一致性、隔离性、持久性）特性；InnoDB也是支持外键（foreign key）的，并且支持细粒度的行级别的锁（row-level locking）。
而MyISAM不支持事务、不支持外键（但其访问速度较快），支持表级别的锁（而不是细粒度的行级别锁）。
Memory存储引擎在较老的MySQL中也叫HEAP，是将所有的数据都存放在内存中的，它具有快速读写的优势，一般存放一些不重要的但需要快速查找的数据（如临时表）。
如下表格来自MySQL官方网站，是一些主流存储引擎的特性比较：
Table 14.1. Storage Engines Feature Summary
| Feature | MyISAM | Memory | InnoDB | Archive | NDB |
|---|---|---|---|---|---|
| Storage limits | 256TB | RAM | 64TB | None | 384EB |
| Transactions | No | No | Yes | No | Yes |
| Locking granularity | Table | Table | Row | Table | Row |
| MVCC | No | No | Yes | No | No |
| Geospatial data type support | Yes | No | Yes | Yes | Yes |
| Geospatial indexing support | Yes | No | No | No | No |
| B-tree indexes | Yes | Yes | Yes | No | No |
| T-tree indexes | No | No | No | No | Yes |
| Hash indexes | No | Yes | No[a] | No | Yes |
| Full-text search indexes | Yes | No | Yes[b] | No | No |
| Clustered indexes | No | No | Yes | No | No |
| Data caches | No | N/A | Yes | No | Yes |
| Index caches | Yes | N/A | Yes | No | Yes |
| Compressed data | Yes[c] | No | Yes[d] | Yes | No |
| Encrypted data[e] | Yes | Yes | Yes | Yes | Yes |
| Cluster database support | No | No | No | No | Yes |
| Replication support[f] | Yes | Yes | Yes | Yes | Yes |
| Foreign key support | No | No | Yes | No | No |
| Backup / point-in-time recovery[g] | Yes | Yes | Yes | Yes | Yes |
| Query cache support | Yes | Yes | Yes | Yes | Yes |
| Update statistics for data dictionary | Yes | Yes | Yes | Yes | Yes |
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[a] InnoDB utilizes hash indexes internally for its Adaptive Hash Index feature. [b] InnoDB support for FULLTEXT indexes is available in MySQL 5.6.4 and higher. [c] Compressed MyISAM tables are supported only when using the compressed row format. Tables using the compressed row format with MyISAM are read only. [d] Compressed InnoDB tables require the InnoDB Barracuda file format. [e] Implemented in the server (via encryption functions), rather than in the storage engine. [f] Implemented in the server, rather than in the storage engine. [g] Implemented in the server, rather than in the storage engine. |
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参考资料：
storage engines: http://dev.mysql.com/doc/refman/5.6/en/storage-engines.html
MyISAM: http://dev.mysql.com/doc/refman/5.6/en/myisam-storage-engine.html
InnoDB: http://dev.mysql.com/doc/refman/5.6/en/innodb-storage-engine.html