Update and correct information aboud sys.schema_unused_indexes (#16885)…

… (#16902)

TOC-tidb-cloud.md

@@ -601,6 +601,9 @@
       - PERFORMANCE_SCHEMA
         - [Overview](/performance-schema/performance-schema.md)
         - [`SESSION_CONNECT_ATTRS`](/performance-schema/performance-schema-session-connect-attrs.md)
+      - SYS
+        - [Overview](/sys-schema/sys-schema.md)
+        - [`schema_unused_indexes`](/sys-schema/sys-schema-unused-indexes.md)
     - [Metadata Lock](/metadata-lock.md)
     - [Use UUIDs](/best-practices/uuid.md)
     - [TiDB Accelerated Table Creation](/accelerated-table-creation.md)

TOC.md

@@ -981,7 +981,9 @@
       - PERFORMANCE_SCHEMA
         - [Overview](/performance-schema/performance-schema.md)
         - [`SESSION_CONNECT_ATTRS`](/performance-schema/performance-schema-session-connect-attrs.md)
-      - [`SYS`](/sys-schema.md)
+      - SYS
+        - [Overview](/sys-schema/sys-schema.md)
+        - [`schema_unused_indexes`](/sys-schema/sys-schema-unused-indexes.md)
     - [Metadata Lock](/metadata-lock.md)
     - [TiDB Accelerated Table Creation](/accelerated-table-creation.md)
   - UI

information-schema/information-schema-tidb-index-usage.md

@@ -101,3 +101,7 @@ The output is as follows:
 
 - The data in the `TIDB_INDEX_USAGE` table might be delayed by up to 5 minutes.
 - After TiDB restarts, the data in the `TIDB_INDEX_USAGE` table is cleared.
+
+## Read more
+
+- [`sys.schema_unused_indexes`](/sys-schema/sys-schema-unused-indexes.md)

information-schema/information-schema.md

@@ -13,7 +13,7 @@ Many `INFORMATION_SCHEMA` tables have a corresponding `SHOW` command. The benefi
 
 <CustomContent platform="tidb">
 
-| Table Name                                                                              | Description                 |
+| Table name                                                                              | Description                 |
 |-----------------------------------------------------------------------------------------|-----------------------------|
 | [`CHARACTER_SETS`](/information-schema/information-schema-character-sets.md)            | Provides a list of character sets the server supports. |
 | [`CHECK_CONSTRAINTS`](/information-schema/information-schema-check-constraints.md)            | Provides information about [`CHECK` constraints](/constraints.md#check) on tables. |
@@ -56,7 +56,7 @@ Many `INFORMATION_SCHEMA` tables have a corresponding `SHOW` command. The benefi
 
 <CustomContent platform="tidb-cloud">
 
-| Table Name                                                                              | Description                 |
+| Table name                                                                              | Description                 |
 |-----------------------------------------------------------------------------------------|-----------------------------|
 | [`CHARACTER_SETS`](/information-schema/information-schema-character-sets.md)            | Provides a list of character sets the server supports. |
 | [`CHECK_CONSTRAINTS`](/information-schema/information-schema-check-constraints.md)            | Provides information about [`CHECK` constraints](/constraints.md#check) on tables. |
@@ -104,7 +104,7 @@ Many `INFORMATION_SCHEMA` tables have a corresponding `SHOW` command. The benefi
 >
 > Some of the following tables are only supported on TiDB Self-Hosted and not supported on TiDB Cloud. To get a full list of unsupported tables on TiDB Cloud, see [System tables](https://docs.pingcap.com/tidbcloud/limited-sql-features#system-tables).
 
-| Table Name                                                                              | Description |
+| Table name                                                                              | Description |
 |-----------------------------------------------------------------------------------------|-------------|
 | [`ANALYZE_STATUS`](/information-schema/information-schema-analyze-status.md)            | Provides information about tasks to collect statistics. |
 | [`CLIENT_ERRORS_SUMMARY_BY_HOST`](/information-schema/client-errors-summary-by-host.md)  | Provides a summary of errors and warnings generated by client requests and returned to clients. |
@@ -157,7 +157,7 @@ Many `INFORMATION_SCHEMA` tables have a corresponding `SHOW` command. The benefi
 
 <CustomContent platform="tidb-cloud">
 
-| Table Name                                                                              | Description |
+| Table name                                                                              | Description |
 |-----------------------------------------------------------------------------------------|-------------|
 | [`ANALYZE_STATUS`](/information-schema/information-schema-analyze-status.md)            | Provides information about tasks to collect statistics. |
 | [`CLIENT_ERRORS_SUMMARY_BY_HOST`](/information-schema/client-errors-summary-by-host.md)  | Provides a summary of errors and warnings generated by client requests and returned to clients. |

performance-schema/performance-schema.md

@@ -9,7 +9,7 @@ TiDB implements performance schema tables for MySQL compatibility.
 
 ## Tables for MySQL compatibility
 
-| Table Name                                                                                       | Description                                               |
+| Table name                                                                                       | Description                                               |
 |--------------------------------------------------------------------------------------------------|-----------------------------------------------------------|
 | `events_stages_current`                                                                          |                                                           |
 | `events_stages_history`                                                                          |                                                           |
@@ -33,7 +33,7 @@ TiDB implements performance schema tables for MySQL compatibility.
 
 ## Tables that are TiDB extensions
 
-| Table Name                                                                                       | Description                                               |
+| Table name                                                                                       | Description                                               |
 |--------------------------------------------------------------------------------------------------|-----------------------------------------------------------|
 | `pd_profile_allocs`                                                                              |                                                           |
 | `pd_profile_block`                                                                               |                                                           |

releases/release-8.0.0.md

@@ -47,7 +47,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v8.0/quick-start-with-
   <tr>
     <td rowspan="1">DB Operations and Observability</td>
     <td>Support monitoring index usage statistics </td>
-    <td>Proper index design is a crucial prerequisite to maintaining database performance. TiDB v8.0.0 introduces the <a href="https://docs.pingcap.com/tidb/v8.0/information-schema-tidb-index-usage"><code>INFORMATION_SCHEMA.TIDB_INDEX_USAGE</code></a> table and the <a href="https://docs.pingcap.com/tidb/v8.0/sys-schema"><code>sys.schema_unused_index</code></a> view to provide usage statistics of indexes. This feature helps you assess the efficiency of indexes in the database and optimize the index design.</td>
+    <td>Proper index design is a crucial prerequisite to maintaining database performance. TiDB v8.0.0 introduces the <a href="https://docs.pingcap.com/tidb/v8.0/information-schema-tidb-index-usage"><code>INFORMATION_SCHEMA.TIDB_INDEX_USAGE</code></a> table and the <a href="https://docs.pingcap.com/tidb/v8.0/sys-schema-unused-indexes"><code>sys.schema_unused_indexes</code></a> view to provide usage statistics of indexes. This feature helps you assess the efficiency of indexes in the database and optimize the index design.</td>
   </tr>
   <tr>
     <td rowspan="2">Data Migration</td>
@@ -236,7 +236,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v8.0/quick-start-with-
 
   With this information, you can identify indexes that are not used by the optimizer and indexes with poor selectivity, thereby optimizing index design to improve database performance.
 
-    Additionally, TiDB v8.0.0 introduces a view [`sys.schema_unused_index`](/sys-schema.md), which is compatible with MySQL. This view shows indexes that have not been used since the last start of TiDB instances. For clusters upgraded from versions earlier than v8.0.0, the `sys` schema and the views are not created automatically. You can manually create them by referring to [`sys`](/sys-schema.md).
+    Additionally, TiDB v8.0.0 introduces a view [`sys.schema_unused_indexes`](/sys-schema/sys-schema-unused-indexes.md), which is compatible with MySQL. This view shows indexes that have not been used since the last start of TiDB instances. For clusters upgraded from versions earlier than v8.0.0, the `sys` schema and the views are not created automatically. You can manually create them by referring to [`sys.schema_unused_indexes`](/sys-schema/sys-schema-unused-indexes.md#manually-create-the-schema_unused_indexes-view).
 
     For more information, see [documentation](/information-schema/information-schema-tidb-index-usage.md).
 
@@ -362,7 +362,7 @@ Quick access: [Quick start](https://docs.pingcap.com/tidb/v8.0/quick-start-with-
 ### System tables
 
 * Add new system tables [`INFORMATION_SCHEMA.TIDB_INDEX_USAGE`](/information-schema/information-schema-tidb-index-usage.md) and [`INFORMATION_SCHEMA.CLUSTER_TIDB_INDEX_USAGE`](/information-schema/information-schema-tidb-index-usage.md#cluster_tidb_index_usage) to record index usage statistics on TiDB nodes.
-* Add a new system schema [`sys`](/sys-schema.md) and a new view [`sys.schema_unused_index`](/sys-schema.md#schema_unused_index), which records indexes that have not been used since the last start of TiDB.
+* Add a new system schema [`sys`](/sys-schema/sys-schema.md) and a new view [`sys.schema_unused_indexes`](/sys-schema/sys-schema-unused-indexes.md), which records indexes that have not been used since the last start of TiDB.
 
 ## Deprecated features
 

sys-schema.md → sys-schema/sys-schema-unused-indexes.md

@@ -1,35 +1,11 @@
 ---
-title: sys Schema
-summary: Learn about the system tables in the `sys` schema.
+title: schema_unused_indexes
+summary: Learn about the `schema_unused_indexes` table in the `sys` schema.
 ---
 
-# `sys` Schema
+# `schema_unused_indexes`
 
-Starting from v8.0.0, TiDB provides the `sys` schema. You can use the views in `sys` schema to understand the data in the system tables, [`INFORMATION_SCHEMA`](/information-schema/information-schema.md), and [`PERFORMANCE SCHEMA`](/performance-schema/performance-schema.md) of TiDB.
-
-## Manually create the `sys` schema and views
-
-For clusters upgraded from versions earlier than v8.0.0, the `sys` schema and the views in it are not created automatically. You can manually create them using the following SQL statements:
-
-```sql
-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;
-```
-
-## `schema_unused_index`
-
-`schema_unused_index` records indexes that have not been used since the last start of TiDB. It includes the following columns:
+`schema_unused_indexes` records indexes that have not been used since the last start of TiDB. It includes the following columns:
 
 - `OBJECT_SCHEMA`: The name of the database to which the table containing the index belongs.
 - `OBJECT_NAME`: The name of the table containing the index.
@@ -51,4 +27,28 @@ The output is as follows:
 | index_name    | varchar(64) | YES  |      | NULL    |       |
 +---------------+-------------+------+------+---------+-------+
 3 rows in set (0.00 sec)
-```
+```
+
+## Manually create the `schema_unused_indexes` view
+
+For clusters upgraded from versions earlier than v8.0.0, the `sys` schema and the views in it are not created automatically. You can manually create them using the following SQL statements:
+
+```sql
+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;
+```
+
+## Read more
+
+- [`INFORMATION_SCHEMA.TIDB_INDEX_USAGE`](/information-schema/information-schema-tidb-index-usage.md)

sys-schema/sys-schema.md

@@ -0,0 +1,14 @@
+---
+title: sys Schema
+summary: Learn about the system tables in the `sys` schema.
+---
+
+# `sys` Schema
+
+Starting from v8.0.0, TiDB provides the `sys` schema. You can use the views in `sys` schema to understand the data in the system tables, [`INFORMATION_SCHEMA`](/information-schema/information-schema.md), and [`PERFORMANCE SCHEMA`](/performance-schema/performance-schema.md) of TiDB.
+
+## Tables for MySQL compatibility
+
+| Table name                                                                                       | Description                                               |
+|--------------------------------------------------------------------------------------------------|-----------------------------------------------------------|
+| [`schema_unused_indexes`](/sys-schema/sys-schema-unused-indexes.md)                                  | Records indexes that have not been used since the last start of TiDB. |