SHOW PLACEMENT FOR

警告：

Placement Rules in SQL 是 TiDB 在 v5.3.0 中引入的实验特性，其语法在 GA 前可能会发生变化，还可能存在 bug。如果你知晓潜在的风险，可通过执行 SET GLOBAL tidb_enable_alter_placement = 1; 来开启该实验特性。

SHOW PLACEMENT FOR 用于汇总直接放置 (direct placement) 和放置策略 (placement policy) 中所有的放置选项，并为特定表、数据库或分区以规范形式呈现这些选项信息。

语法图

1. ShowStmt ::=
2. "PLACEMENT" "FOR" ShowPlacementTarget

4. ShowPlacementTarget ::=
5. DatabaseSym DBName
6. |   "TABLE" TableName
7. |   "TABLE" TableName "PARTITION" Identifier

示例

1. CREATE PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1" FOLLOWERS=4;
2. use test;
3. ALTER DATABASE test PLACEMENT POLICY=p1;
4. CREATE TABLE t1 (a INT);
5. CREATE TABLE t2 (a INT) PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1" FOLLOWERS=4;
6. SHOW PLACEMENT FOR DATABASE test;
7. SHOW PLACEMENT FOR TABLE t1;
8. SHOW CREATE TABLE t1\G
9. SHOW PLACEMENT FOR TABLE t2;
10. CREATE TABLE t3 (a INT) PARTITION BY RANGE (a) (PARTITION p1 VALUES LESS THAN (10), PARTITION p2 VALUES LESS THAN (20) FOLLOWERS=4);
11. SHOW PLACEMENT FOR TABLE t3 PARTITION p1;
12. SHOW PLACEMENT FOR TABLE t3 PARTITION p2;

1. Query OK, 0 rows affected (0.02 sec)

3. Query OK, 0 rows affected (0.00 sec)

5. Query OK, 0 rows affected (0.00 sec)

7. Query OK, 0 rows affected (0.01 sec)

9. +---------------+----------------------------------------------------------------------+------------------+
10. | Target        | Placement                                                            | Scheduling_State |
11. +---------------+----------------------------------------------------------------------+------------------+
12. | DATABASE test | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1" FOLLOWERS=4 | INPROGRESS       |
13. +---------------+----------------------------------------------------------------------+------------------+
14. 1 row in set (0.00 sec)

16. +---------------+-------------+------------------+
17. | Target        | Placement   | Scheduling_State |
18. +---------------+-------------+------------------+
19. | TABLE test.t1 | FOLLOWERS=4 | INPROGRESS       |
20. +---------------+-------------+------------------+
21. 1 row in set (0.00 sec)

23. *************************** 1. row ***************************
24. Table: t1
25. Create Table: CREATE TABLE `t1` (
26. `a` int(11) DEFAULT NULL
27. ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin /*T![placement] PLACEMENT POLICY=`p1` */
28. 1 row in set (0.00 sec)

30. +---------------+----------------------------------------------------------------------+------------------+
31. | Target        | Placement                                                            | Scheduling_State |
32. +---------------+----------------------------------------------------------------------+------------------+
33. | TABLE test.t2 | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1" FOLLOWERS=4 | INPROGRESS       |
34. +---------------+----------------------------------------------------------------------+------------------+
35. 1 row in set (0.00 sec)

37. Query OK, 0 rows affected (0.14 sec)

39. +----------------------------+-----------------------------------------------------------------------+------------------+
40. | Target                     | Placement                                                             | Scheduling_State |
41. +----------------------------+-----------------------------------------------------------------------+------------------+
42. | TABLE test.t3 PARTITION p1 | PRIMARY_REGION="us-east-1" REGIONS="us-east-1,,us-west-1" FOLLOWERS=4 | INPROGRESS       |
43. +----------------------------+-----------------------------------------------------------------------+------------------+
44. 1 row in set (0.00 sec)

46. +----------------------------+-------------+------------------+
47. | Target                     | Placement   | Scheduling_State |
48. +----------------------------+-------------+------------------+
49. | TABLE test.t3 PARTITION p2 | FOLLOWERS=4 | INPROGRESS       |
50. +----------------------------+-------------+------------------+
51. 1 row in set (0.00 sec)

MySQL 兼容性

该语句是 TiDB 对 MySQL 语法的扩展。

另请参阅