ALTER PLACEMENT POLICY

ALTER PLACEMENT POLICY 用于修改已创建的放置策略。此修改会自动更新至所有使用这些放置策略的表和分区。

ALTER PLACEMENT POLICY 会完全替换之前定义的规则，而不会和之前的规则合并，比如在下面的例子中，FOLLOWERS=4 就被 ALTER PLACEMENT POLICY 语句覆盖了：

1. CREATE PLACEMENT POLICY p1 FOLLOWERS=4;
2. ALTER PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1";

语法图

AlterPolicyStmt

ALTER PLACEMENT POLICY - 图1

PolicyName

ALTER PLACEMENT POLICY - 图2

PlacementOptionList

ALTER PLACEMENT POLICY - 图3

PlacementOption

ALTER PLACEMENT POLICY - 图4

CommonPlacementOption

ALTER PLACEMENT POLICY - 图5

SugarPlacementOption

ALTER PLACEMENT POLICY - 图6

AdvancedPlacementOption

ALTER PLACEMENT POLICY - 图7

1. AlterPolicyStmt ::=
2. "ALTER" "PLACEMENT" "POLICY" IfExists PolicyName PlacementOptionList

4. PolicyName ::=
5. Identifier

7. PlacementOptionList ::=
8. PlacementOption
9. |   PlacementOptionList PlacementOption
10. |   PlacementOptionList ',' PlacementOption

12. PlacementOption ::=
13. CommonPlacementOption
14. |   SugarPlacementOption
15. |   AdvancedPlacementOption

17. CommonPlacementOption ::=
18. "FOLLOWERS" EqOpt LengthNum

20. SugarPlacementOption ::=
21. "PRIMARY_REGION" EqOpt stringLit
22. |   "REGIONS" EqOpt stringLit
23. |   "SCHEDULE" EqOpt stringLit

25. AdvancedPlacementOption ::=
26. "LEARNERS" EqOpt LengthNum
27. |   "CONSTRAINTS" EqOpt stringLit
28. |   "LEADER_CONSTRAINTS" EqOpt stringLit
29. |   "FOLLOWER_CONSTRAINTS" EqOpt stringLit
30. |   "LEARNER_CONSTRAINTS" EqOpt stringLit
31. |   "SURVIVAL_PREFERENCES" EqOpt stringLit

示例

ALTER PLACEMENT POLICY - 图8

注意

如要查看所在集群中可用的区域，见 SHOW PLACEMENT LABELS。如果未看到任何可用的区域，此 TiKV 集群在部署时可能未正确设置标签 (label)。

1. CREATE PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1";
2. CREATE TABLE t1 (i INT) PLACEMENT POLICY=p1; -- 绑定放置策略 p1 到表 t1。
3. ALTER PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1,us-west-2" FOLLOWERS=4; -- t1 上的放置规则会自动更新。
4. SHOW CREATE PLACEMENT POLICY p1\G

1. Query OK, 0 rows affected (0.08 sec)

3. Query OK, 0 rows affected (0.10 sec)

5. ***************************[ 1. row ]***************************
6. Policy        | p1
7. Create Policy | CREATE PLACEMENT POLICY `p1` PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1,us-west-2" FOLLOWERS=4
8. 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