add doc for information_schema.variables_info (pingcap#10712)

* add doc for information_schema.variables_info * add toc and fix link * Update information-schema/information-schema.md * Update information-schema/information-schema-variables-info.md Co-authored-by: Ran <huangran.alex@gmail.com> * Update information-schema/information-schema-variables-info.md Co-authored-by: Ran <huangran.alex@gmail.com> * variables_scope -> variable_scope * Apply suggestions from code review Co-authored-by: shichun-0415 <89768198+shichun-0415@users.noreply.github.com> Co-authored-by: Ran <huangran.alex@gmail.com> Co-authored-by: shichun-0415 <89768198+shichun-0415@users.noreply.github.com>
shawn0915 · Aug 2, 2022 · b6548c2 · b6548c2
1 parent 6181bee
commit b6548c2
Show file tree

Hide file tree

Showing 3 changed files with 57 additions and 0 deletions.
diff --git a/TOC.md b/TOC.md
@@ -818,6 +818,7 @@
         - [`TIKV_REGION_STATUS`](/information-schema/information-schema-tikv-region-status.md)
         - [`TIKV_STORE_STATUS`](/information-schema/information-schema-tikv-store-status.md)
         - [`USER_PRIVILEGES`](/information-schema/information-schema-user-privileges.md)
+        - [`VARIABLES_INFO`](/information-schema/information-schema-variables-info.md)
         - [`VIEWS`](/information-schema/information-schema-views.md)
       - [`METRICS_SCHEMA`](/metrics-schema.md)
   - UI

diff --git a/information-schema/information-schema-variables-info.md b/information-schema/information-schema-variables-info.md
@@ -0,0 +1,55 @@
+---
+title: VARIABLES_INFO
+summary: 了解 information_schema 表 `VARIABLES_INFO`。
+---
+
+# VARIABLES_INFO
+
+`VARIABLES_INFO` 可用于查看当前 TiDB 集群或实例的系统变量默认值、当前值以及作用域等信息。
+
+```sql
+USE information_schema;
+DESC variables_info;
+```
+
+```sql
++-----------------+---------------------+------+------+---------+-------+
+| Field           | Type                | Null | Key  | Default | Extra |
++-----------------+---------------------+------+------+---------+-------+
+| VARIABLE_NAME   | varchar(64)         | NO   |      | NULL    |       |
+| VARIABLE_SCOPE  | varchar(64)         | NO   |      | NULL    |       |
+| DEFAULT_VALUE   | varchar(64)         | NO   |      | NULL    |       |
+| CURRENT_VALUE   | varchar(64)         | NO   |      | NULL    |       |
+| MIN_VALUE       | bigint(64)          | YES  |      | NULL    |       |
+| MAX_VALUE       | bigint(64) unsigned | YES  |      | NULL    |       |
+| POSSIBLE_VALUES | varchar(256)        | YES  |      | NULL    |       |
+| IS_NOOP         | varchar(64)         | NO   |      | NULL    |       |
++-----------------+---------------------+------+------+---------+-------+
+8 rows in set (0.00 sec)
+```
+
+```sql
+SELECT * FROM variables_info ORDER BY variable_name LIMIT 3;
+```
+
+```sql
++-----------------------------------+----------------+---------------+---------------+-----------+-----------+-----------------+---------+
+| VARIABLE_NAME                     | VARIABLE_SCOPE | DEFAULT_VALUE | CURRENT_VALUE | MIN_VALUE | MAX_VALUE | POSSIBLE_VALUES | IS_NOOP |
++-----------------------------------+----------------+---------------+---------------+-----------+-----------+-----------------+---------+
+| allow_auto_random_explicit_insert | SESSION,GLOBAL | OFF           | OFF           |      NULL |      NULL | NULL            | NO      |
+| auto_increment_increment          | SESSION,GLOBAL | 1             | 1             |         1 |     65535 | NULL            | NO      |
+| auto_increment_offset             | SESSION,GLOBAL | 1             | 1             |         1 |     65535 | NULL            | NO      |
++-----------------------------------+----------------+---------------+---------------+-----------+-----------+-----------------+---------+
+3 rows in set (0.01 sec)
+```
+
+`VARIABLES_INFO` 表中列的含义如下：
+
+* `VARIABLE_NAME`：系统变量名称。
+* `VARIABLE_SCOPE`：系统变量的作用域。`SESSION` 表示当前 session 可见；`INSTANCE` 表示当前 TiDB 实例可见；`GLOBAL` 表示集群内可见。
+* `DEFAULT_VALUE`：系统变量的默认值。
+* `CURRENT_VALUE`：系统变量的当前值。如果应用范围中包含 `SESSION`，则显示当前 session 的值。
+* `MIN_VALUE`：数值类型的系统变量允许的最小值。如果变量值为非数值类型，则为 NULL。
+* `MAX_VALUE`：数值类型的系统变量允许的最大值。如果变量值为非数值类型，则为 NULL。
+* `POSSIBLE_VALUES`：系统变量所有可能的值。如果变量值不可枚举，则为 NULL。
+* `IS_NOOP`：是否为 `noop` 的系统变量。
diff --git a/information-schema/information-schema.md b/information-schema/information-schema.md
@@ -44,6 +44,7 @@ Information Schema 提供了一种查看系统元数据的 ANSI 标准方法。
 | `TABLE_PRIVILEGES`                                                                                                         | TiDB 未实现，返回零行。                                                           |
 | `TRIGGERS`                                                                                                                 | TiDB 未实现，返回零行。                                                           |
 | [`USER_PRIVILEGES`](/information-schema/information-schema-user-privileges.md)                                             | 汇总与当前用户相关的权限。                                                        |
+| [`VARIABLES_INFO`](/information-schema/information-schema-variables-info.md)                                               | 提供 TiDB 系统变量的信息。                                               |
 | [`VIEWS`](/information-schema/information-schema-views.md)                                                                 | 提供当前用户可见的视图列表。类似于 `SHOW FULL TABLES WHERE table_type = 'VIEW'`。 |
 
 ## TiDB 中的扩展表