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。
语法图
- AlterPolicyStmt
- PolicyName
- PlacementOptionList
- DirectPlacementOption
AlterPolicyStmt ::=
"ALTER" "PLACEMENT" "POLICY" IfExists PolicyName PlacementOptionList
PolicyName ::=
Identifier
PlacementOptionList ::=
DirectPlacementOption
| PlacementOptionList DirectPlacementOption
| PlacementOptionList ',' DirectPlacementOption
DirectPlacementOption ::=
"PRIMARY_REGION" EqOpt stringLit
| "REGIONS" EqOpt stringLit
| "FOLLOWERS" EqOpt LengthNum
| "VOTERS" EqOpt LengthNum
| "LEARNERS" EqOpt LengthNum
| "SCHEDULE" EqOpt stringLit
| "CONSTRAINTS" EqOpt stringLit
| "LEADER_CONSTRAINTS" EqOpt stringLit
| "FOLLOWER_CONSTRAINTS" EqOpt stringLit
| "VOTER_CONSTRAINTS" EqOpt stringLit
| "LEARNER_CONSTRAINTS" EqOpt stringLit
示例
CREATE PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1";
ALTER PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1,us-west-2" FOLLOWERS=4;
SHOW CREATE PLACEMENT POLICY p1\G
Query OK, 0 rows affected (0.08 sec)
Query OK, 0 rows affected (0.10 sec)
*************************** 1. row ***************************
Policy: p1
Create Policy: CREATE PLACEMENT POLICY `p1` PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1,us-west-2" FOLLOWERS=4
1 row in set (0.00 sec)
MySQL 兼容性
该语句是 TiDB 对 MySQL 语法的扩展。