schema_unused_indexes

schema_unused_indexes 记录自上次启动 TiDB 以来未被使用的索引。它包含以下列：

• OBJECT_SCHEMA：包含该索引的表所在的数据库名称。
• OBJECT_NAME：包含索引的表的名称。
• INDEX_NAME：索引的名称。

USE SYS;
DESC SCHEMA_UNUSED_INDEXES;

输出结果如下：

+---------------+-------------+------+------+---------+-------+
| Field         | Type        | Null | Key  | Default | Extra |
+---------------+-------------+------+------+---------+-------+
| object_schema | varchar(64) | YES  |      | NULL    |       |
| object_name   | varchar(64) | YES  |      | NULL    |       |
| index_name    | varchar(64) | YES  |      | NULL    |       |
+---------------+-------------+------+------+---------+-------+
3 rows in set (0.00 sec)

手动创建 schema_unused_indexes 视图

对于从版本早于 v8.0.0 升级的集群，sys 模式及其视图不会自动创建。你可以使用以下 SQL 语句手动创建：

CREATE DATABASE IF NOT EXISTS sys;
CREATE OR REPLACE VIEW sys.schema_unused_indexes AS
  SELECT
    table_schema as object_schema,
    table_name as object_name,
    index_name
  FROM information_schema.cluster_tidb_index_usage
  WHERE
    table_schema not in ('sys', 'mysql', 'INFORMATION_SCHEMA', 'PERFORMANCE_SCHEMA') and
    index_name != 'PRIMARY'
  GROUP BY table_schema, table_name, index_name
  HAVING
    sum(last_access_time) is null;

了解更多

• INFORMATION_SCHEMA.TIDB_INDEX_USAGE