尝试对mysiam表（1500万）删除索引失败
#uk表字段类型比较简单，都是int/tinyint/timestamp类型。
CREATE TABLE `uk` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`a` int(11) NOT NULL DEFAULT '0',
`b` int(11) NOT NULL,
`c` int(11) NOT NULL DEFAULT '0',
`d` int(11) NOT NULL DEFAULT '0',
`e` int(11) DEFAULT '0',
`f` tinyint(4) NOT NULL DEFAULT '1',
`l` timestamp NOT NULL DEFAULT ‘0’ ,
PRIMARY KEY (`id`),
UNIQUE KEY `idx_a_b_c` (`a`,`b`,`c`),
KEY `idx_f` (`f`)
) ENGINE=MyISAM AUTO_INCREMENT=15000000 DEFAULT CHARSET=utf8;
#尝试允许并发删除索引
alter table uk drop index idx_a_b_c , ALGORITHM=INPLACE/LOCK=NONE;
ERROR 1845 (0A000): ALGORITHM=INPLACE is not supported for this operation. Try ALGORITHM=COPY.
ERROR 1845 (0A000): LOCK=NONE is not supported for this operation. Try LOCK=SHARED.
#直接对myisam表进行DDL操作
alter table uk drop index idx_a_b_c;
#耗时2 min 43.27 sec（普通磁盘）
alter table uk add index idx_a_b(a,b);
#耗时2 min 43.27 sec（普通磁盘）
alter table uk add index idx_a_b(a,b);
Query OK, rows affected (2 min 46.98 sec)
#修改引擎为innodb,过程很慢
alter table uk engine=innodb;
21 min 45.81 sec
#尝试删除索引
alter table uk drop index idx_a_b_c, ALGORITHM=INPLACE;
Query OK, 0 rows affected (0.14 sec)
#尝试重建索引
alter table uk add index idx_a_b(a,b), ALGORITHM=INPLACE;
Query OK, 0 rows affected (1 min 58.82 sec)
Records: 0 Duplicates: 0 Warnings: 0
2016-11-29