MySQL 8 新特性之Invisible Indexes

mysql> show create table sys.schema_unused_indexes\G
*************************** 1. row ***************************
        View: schema_unused_indexes
    Create View: CREATE ALGORITHM=MERGE DEFINER=`mysql.sys`@`localhost` SQL SECURITY INVOKER VIEW `sys`.`schema_unused_indexes` (
`object_schema`,`object_name`,`index_name`) AS select `t`.`OBJECT_SCHEMA` AS `object_schema`,`t`.`OBJECT_NAME` AS `object_name`,`t`.`INDEX_NAME` AS `index_name` from (`performance_schema`.`table_io_waits_summary_by_index_usage` `t` join `information_schema`.`STATISTICS` `s` on(((`t`.`OBJECT_SCHEMA` = convert(`s`.`TABLE_SCHEMA` using utf8mb4)) and (`t`.`OBJECT_NAME` = convert(`s`.`TABLE_NAME` using utf8mb4)) and (convert(`t`.`INDEX_NAME` using utf8) = `s`.`INDEX_NAME`)))) where ((`t`.`INDEX_NAME` is not null) and (`t`.`COUNT_STAR` = 0) and (`t`.`OBJECT_SCHEMA` <> 'mysql') and (`t`.`INDEX_NAME` <> 'PRIMARY') and (`s`.`NON_UNIQUE` = 1) and (`s`.`SEQ_IN_INDEX` = 1)) order by `t`.`OBJECT_SCHEMA`,`t`.`OBJECT_NAME`character_set_client: utf8mb4
collation_connection: utf8mb4_0900_ai_ci
1 row in set, 1 warning (0.00 sec)

mysql> show create table slowtech.t1\G
*************************** 1. row ***************************
   Table: t1
Create Table: CREATE TABLE `t1` (
 `id` int(11) NOT NULL,
 `name` varchar(10) DEFAULT NULL,
 PRIMARY KEY (`id`),
 KEY `idx_name` (`name`) /*!80000 INVISIBLE */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
mysql> explain select * from slowtech.t1 where name='a';
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra   |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| 1 | SIMPLE   | t1  | NULL   | ALL | NULL     | NULL | NULL  | NULL |  6 |  16.67 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)
mysql> set session optimizer_switch="use_invisible_indexes=on";
Query OK, 0 rows affected (0.00 sec)

mysql> explain select * from slowtech.t1 where name='a';
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key   | key_len | ref | rows | filtered | Extra   |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------------+
| 1 | SIMPLE   | t1  | NULL   | ref | idx_name   | idx_name | 43   | const |  1 | 100.00 | Using index |
+----+-------------+-------+------------+------+---------------+----------+---------+-------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

create table t1(id int primary key,name varchar(10),index idx_name (name) invisible);
alter table t1 alter index idx_name visible;
alter table t1 alter index idx_name invisible;

mysql> select table_schema,table_name,index_name,column_name,is_visible from information_schema.statistics where is_visible='no';
+--------------+------------+------------+-------------+------------+
| TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | COLUMN_NAME | IS_VISIBLE |
+--------------+------------+------------+-------------+------------+
| slowtech  | t1    | idx_name | name    | NO    |
+--------------+------------+------------+-------------+------------+
1 row in set (0.00 sec)