Add documents for information_schema.tidb_index_usage and sys.schema_unused_index.
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| --- | ||
| title: TIDB_INDEX_USAGE | ||
| summary: 了解 INFORMATION_SCHEMA 表 `TIDB_INDEX_USAGE`。 | ||
| --- | ||
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| # TIDB_INDEX_USAGE | ||
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| TiDB 从 v8.0.0 开始提供 `TIDB_INDEX_USAGE` 表，你可以使用该表查看当前 TiDB 节点中所有索引的访问统计信息。在 SQL 语句执行时，TiDB 默认维护访问索引有关的统计信息，可以通过修改配置项 [`instance.tidb_enable_collect_execution_info`](/tidb-configuration-file.md#tidb_enable_collect_execution_info) 或者系统变量 [`tidb_enable_collect_execution_info`](/system-variables.md#tidb_enable_collect_execution_info) 将其关闭。 | ||
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| ```sql | ||
| USE INFORMATION_SCHEMA; | ||
| DESC TIDB_INDEX_USAGE; | ||
| ``` | ||
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| ```sql | ||
| +--------------------------+-------------+------+------+---------+-------+ | ||
| | Field | Type | Null | Key | Default | Extra | | ||
| +--------------------------+-------------+------+------+---------+-------+ | ||
| | TABLE_SCHEMA | varchar(64) | YES | | NULL | | | ||
| | TABLE_NAME | varchar(64) | YES | | NULL | | | ||
| | INDEX_NAME | varchar(64) | YES | | NULL | | | ||
| | QUERY_TOTAL | bigint(21) | YES | | NULL | | | ||
| | KV_REQ_TOTAL | bigint(21) | YES | | NULL | | | ||
| | ROWS_ACCESS_TOTAL | bigint(21) | YES | | NULL | | | ||
| | PERCENTAGE_ACCESS_0 | bigint(21) | YES | | NULL | | | ||
| | PERCENTAGE_ACCESS_0_1 | bigint(21) | YES | | NULL | | | ||
| | PERCENTAGE_ACCESS_1_10 | bigint(21) | YES | | NULL | | | ||
| | PERCENTAGE_ACCESS_10_20 | bigint(21) | YES | | NULL | | | ||
| | PERCENTAGE_ACCESS_20_50 | bigint(21) | YES | | NULL | | | ||
| | PERCENTAGE_ACCESS_50_100 | bigint(21) | YES | | NULL | | | ||
| | PERCENTAGE_ACCESS_100 | bigint(21) | YES | | NULL | | | ||
| | LAST_ACCESS_TIME | datetime | YES | | NULL | | | ||
| +--------------------------+-------------+------+------+---------+-------+ | ||
| 14 rows in set (0.00 sec) | ||
| ``` | ||
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| `TIDB_INDEX_USAGE` 表中列的含义如下： | ||
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| * `TABLE_SCHEMA`：索引所在表的所属数据库的名称。 | ||
| * `TABLE_NAME`：索引所在表的名称。 | ||
| * `INDEX_NAME`：索引的名称。 | ||
| * `QUERY_TOTAL`：访问该索引的语句总数。 | ||
| * `KV_REQ_TOTAL`：访问该索引时产生的 KV 请求总数。 | ||
| * `ROWS_ACCESS_TOTAL`：访问该索引时扫描的总行数。 | ||
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There was a problem hiding this comment. 对于大表，这个字段一直累加会不会有溢出的风险？需要特殊说明吗 There was a problem hiding this comment. 假设集群每秒钟总共扫描 0xFFFFFFFF 行，uint64 在 0xFFFFFFFF s = 136.19252 年的时候才会溢出，现在看应该没啥风险 🤔 。 |
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| * `PERCENTAGE_ACCESS_0`：行访问比例（访问行数占表总行数的百分比）为 0 的次数。 | ||
| * `PERCENTAGE_ACCESS_0_1`：行访问比例为 0 到 1% 的次数。 | ||
| * `PERCENTAGE_ACCESS_1_10`：行访问比例为 1% 到 10% 的次数。 | ||
| * `PERCENTAGE_ACCESS_10_20`：行访问比例为 10% 到 20% 的次数。 | ||
| * `PERCENTAGE_ACCESS_20_50`：行访问比例为 20% 到 50% 的次数。 | ||
| * `PERCENTAGE_ACCESS_50_100`：行访问比例为 50% 到 100% 的次数。 | ||
| * `PERCENTAGE_ACCESS_100`：行访问比例为 100% 的次数。 | ||
| * `LAST_ACCESS_TIME`：最近一次访问该索引的时间。 | ||
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| ## CLUSTER_TIDB_INDEX_USAGE | ||
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| `TIDB_INDEX_USAGE` 表仅提供单个 TiDB 节点中所有索引的访问统计信息。如果要查看整个集群上所有 TiDB 节点中索引的访问统计信息，需要查询 `CLUSTER_TIDB_INDEX_USAGE` 表。 | ||
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| 与 `TIDB_INDEX_USAGE` 表的查询结果相比，`CLUSTER_TIDB_INDEX_USAGE` 表的查询结果额外包含了 `INSTANCE` 字段。`INSTANCE` 字段展示了集群中各节点的 IP 地址和端口，用于区分不同节点上的统计信息。 | ||
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| ```sql | ||
| USE INFORMATION_SCHEMA; | ||
| DESC CLUSTER_TIDB_INDEX_USAGE; | ||
| ``` | ||
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| 输出结果如下： | ||
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| ```sql | ||
| +-------------------------+-----------------------------------------------------------------+------+------+---------+-------+ | ||
| | Field | Type | Null | Key | Default | Extra | | ||
| +-------------------------+-----------------------------------------------------------------+------+------+---------+-------+ | ||
| | INSTANCE | varchar(64) | YES | | NULL | | | ||
| | ID | bigint(21) unsigned | NO | PRI | NULL | | | ||
| | START_TIME | timestamp(6) | YES | | NULL | | | ||
| | CURRENT_SQL_DIGEST | varchar(64) | YES | | NULL | | | ||
| | CURRENT_SQL_DIGEST_TEXT | text | YES | | NULL | | | ||
| | STATE | enum('Idle','Running','LockWaiting','Committing','RollingBack') | YES | | NULL | | | ||
| | WAITING_START_TIME | timestamp(6) | YES | | NULL | | | ||
| | MEM_BUFFER_KEYS | bigint(64) | YES | | NULL | | | ||
| | MEM_BUFFER_BYTES | bigint(64) | YES | | NULL | | | ||
| | SESSION_ID | bigint(21) unsigned | YES | | NULL | | | ||
| | USER | varchar(16) | YES | | NULL | | | ||
| | DB | varchar(64) | YES | | NULL | | | ||
| | ALL_SQL_DIGESTS | text | YES | | NULL | | | ||
| | RELATED_TABLE_IDS | text | YES | | NULL | | | ||
| | WAITING_TIME | double | YES | | NULL | | | ||
| +-------------------------+-----------------------------------------------------------------+------+------+---------+-------+ | ||
| 15 rows in set (0.00 sec) | ||
| ``` | ||
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| ## 使用限制 | ||
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| - `TIDB_INDEX_USAGE` 表中的数据可能存在最多 5 分钟的延迟。 | ||
| - 在 TiDB 重启后，`TIDB_INDEX_USAGE` 表中的数据会被清空。 | ||
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| Original file line number | Diff line number | Diff line change |
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| --- | ||
| title: sys Schema | ||
| summary: 了解 TiDB `sys` 系统数据库。 | ||
| --- | ||
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| # `sys` Schema | ||
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| TiDB 从 v8.0.0 开始提供 `sys` Schema。你可以通过查看 `sys` 系统数据库中的表或视图理解 TiDB 的系统表、[`INFORMATION_SCHEMA`](/information-schema/information-schema.md) 表和 [`PERFORMANCE SCHEMA`](/performance-schema/performance-schema.md) 表内的数据。 | ||
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| ## 手动创建 `sys` Schema 和视图 | ||
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| 对于从 v8.0.0 之前版本升级的集群，`sys` Schema 和其中的视图不会自动创建。你可以通过以下 SQL 语句手动创建： | ||
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| ```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; | ||
| ``` | ||
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| ## `schema_unused_index` | ||
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| `schema_unused_index` 用于记录自 TiDB 上次启动以来未被使用的索引信息，包括如下列： | ||
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| - `OBJECT_SCHEMA`：索引所在表的所属数据库的名称。 | ||
| - `OBJECT_NAME`：索引所在表的名称。 | ||
| - `INDEX_NAME`：索引的名称。 | ||
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| ```sql | ||
| USE SYS; | ||
| DESC SCHEMA_UNUSED_INDEXES; | ||
| ``` | ||
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| 输出结果如下： | ||
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| ```sql | ||
| +---------------+-------------+------+------+---------+-------+ | ||
| | 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) | ||
| ``` | ||
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