MySQL8.0 索引优化invisible index详情

— 创建测试表
mysql> create table t1(i int ,j int);
Query OK, 0 rows affected (0.03 sec)

— 创建索引
mysql>
mysql> create index idx_i on t1(i);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> — 创建 一个隐藏索引
mysql> create index idx_j on t1(j) invisible ;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

— 查看索引
mysql> show index from t1\G
*************************** 1. row ***************************
Table: t1
Non_unique: 1
Key_name: idx_i
Seq_in_index: 1
Column_name: i
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
Index_comment:
Visible: YES
Expression: NULL
*************************** 2. row ***************************
Table: t1
Non_unique: 1
Key_name: idx_j
Seq_in_index: 1
Column_name: j
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
Index_comment:
Visible: NO
Expression: NULL
2 rows in set (0.00 sec)

mysql> explain select * from t1 where i= 10\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: t1
partitions: NULL
type: ref
possible_keys: idx_i
key: idx_i
key_len: 5
ref: const
rows: 1
filtered: 100.00
Extra: NULL
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from t1 where j= 10\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: t1
partitions: NULL
type: ALL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: 1
filtered: 100.00
Extra: Using where
1 row in set, 1 warning (0.00 sec)

mysql> select @@optimizer_switch\G
*************************** 1. row ***************************
@@optimizer_switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,duplicateweedout=on,subquery_materialization_cost_based=on,use_index_extensions=on,condition_fanout_filter=on,derived_merge=on,use_invisible_indexes=off,skip_scan=on
1 row in set (0.00 sec)

— 设置开关
mysql> set session optimizer_switch=’use_invisible_indexes=on’;
Query OK, 0 rows affected (0.00 sec)
mysql> select @@optimizer_switch\G
*************************** 1. row ***************************
@@optimizer_switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,duplicateweedout=on,subquery_materialization_cost_based=on,use_index_extensions=on,condition_fanout_filter=on,derived_merge=on,use_invisible_indexes=on,skip_scan=on
1 row in set (0.00 sec)

— 此时可以看到 优化器已经可以看到这个索引啦
mysql> explain select * from t1 where j= 10\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: t1
partitions: NULL
type: ref
possible_keys: idx_j
key: idx_j
key_len: 5
ref: const
rows: 1
filtered: 100.00
Extra: NULL
1 row in set, 1 warning (0.00 sec)

mysql> ALTER TABLE t1 ALTER INDEX idx_j INVISIBLE;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> ALTER TABLE t1 ALTER INDEX idx_j VISIBLE;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

create table t2(`id` int not null auto_increment, primary key (`id`));

mysql> show index from t2\G
*************************** 1. row ***************************
Table: t2
Non_unique: 0
Key_name: PRIMARY
Seq_in_index: 1
Column_name: id
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
Index_comment:
Visible: YES
Expression: NULL
1 row in set (0.01 sec)

mysql> alter table t2 alter index PRIMARY key(`id`) invisible;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘PRIMARY invisible’ at line 1

mysql> create table t3(id int not null);
Query OK, 0 rows affected (0.03 sec)

mysql> alter table t3 add primary key pk_t3(id) invisible;
ERROR 3522 (HY000): A primary key index cannot be invisible