什么是存储引擎？
存储引擎是指表的类型，数据库的存储类型决定了表在计算机中的存储方式， 用户可以根据不同的存储方式，是否进行事务处理等来选择合适的存储引擎。
查看数据库支持的存储引擎：
mysql> SHOW ENGINES; +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | Engine | Support | Comment | Transactions | XA | Savepoints | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ | FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL | | MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO | | MyISAM | YES | MyISAM storage engine | NO | NO | NO | | BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO | | CSV | YES | CSV storage engine | NO | NO | NO | | MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO | | ARCHIVE | YES | Archive storage engine | NO | NO | NO | | InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES | | PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO | +--------------------+---------+----------------------------------------------------------------+--------------+------+------------+ 9 rows in set (0.03 sec)
这样看起来很乱，可以加上\G, 让它显示的好看一些：
mysql> SHOW ENGINES\G; *************************** 1. row *************************** Engine: FEDERATED #存储引擎的名称 Support: NO #NO代表不支持 Comment: Federated MySQL storage engine #表示对存储引擎的特点 Transactions: NULL #是否支持事务处理，YES代表支持 XA: NULL #是否是分布式处理规范，YES代表支持 Savepoints: NULL #是否支持保存点，YES代表支持 *************************** 2. row *************************** Engine: MRG_MYISAM Support: YES Comment: Collection of identical MyISAM tables Transactions: NO XA: NO Savepoints: NO *************************** 3. row *************************** Engine: MyISAM Support: YES Comment: MyISAM storage engine Transactions: NO XA: NO Savepoints: NO *************************** 4. row *************************** Engine: BLACKHOLE Support: YES Comment: /dev/null storage engine (anything you write to it disappears) Transactions: NO XA: NO Savepoints: NO *************************** 5. row *************************** Engine: CSV Support: YES Comment: CSV storage engine Transactions: NO XA: NO Savepoints: NO *************************** 6. row *************************** Engine: MEMORY Support: YES Comment: Hash based, stored in memory, useful for temporary tables Transactions: NO XA: NO Savepoints: NO *************************** 7. row *************************** Engine: ARCHIVE Support: YES Comment: Archive storage engine Transactions: NO XA: NO Savepoints: NO *************************** 8. row *************************** Engine: InnoDB Support: DEFAULT Comment: Supports transactions, row-level locking, and foreign keys Transactions: YES XA: YES Savepoints: YES *************************** 9. row *************************** Engine: PERFORMANCE_SCHEMA Support: YES Comment: Performance Schema Transactions: NO XA: NO Savepoints: NO 9 rows in set (0.00 sec) ERROR: No query specified
查看mysql支持的存储引擎：
mysql> SHOW VARIABLES LIKE 'have%'; +----------------------+----------+ | Variable_name | Value | +----------------------+----------+ | have_compress | YES | | have_crypt | NO | | have_csv | YES | | have_dynamic_loading | YES | | have_geometry | YES | | have_innodb | YES | | have_ndbcluster | NO | | have_openssl | DISABLED | | have_partitioning | YES | | have_profiling | YES | | have_query_cache | YES | | have_rtree_keys | YES | | have_ssl | DISABLED | | have_symlink | YES | +----------------------+----------+ 14 rows in set (0.00 sec)
查看默认使用的存储引擎：
mysql> SHOW VARIABLES LIKE 'storage_engine'; +----------------+--------+ | Variable_name | Value | +----------------+--------+ | storage_engine | InnoDB | +----------------+--------+ 1 row in set (0.00 sec)
mysql常用存储引擎及特点：
InnoDB存储引擎：
1. 提供了事务，包括回滚，修复，多版本并发控制的事务安全
2. 支持外键
3. 表结构存储在.frm文件中
4. 数据和索引存储在InnoDB_datahome_dir和InnoDB_datafile_path定义的表空间中
5. 读写效率低，占用的数据空间比较大
mysam存储引擎：
1. 表存储成三个文件，文件名与表名相同 .frm 表结构 .myd 数据 .myi 索引
2. 三种方式：静态型，动态型， 压缩型
3. 占用磁盘空间小，处理速度快，不支持事务，没有事务安全性及并发性处理
memory存储引擎：
1. 使用内存中的数据创建的表，所有数据也都存在内存中
2. 每个表实际对应一个磁盘文件，文件名为.frm, 只存储表结构，数据在内存中
3. 提高表的处理效率，速度快
4. 需要的内存空间大，如果不使用了，需要删除以释放内存
5. 断电数据就没了， 不能建立太大的表
同一个数据库中可以使用多种存储引擎。