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:

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

语法图

AlterPolicyStmt
ALTERPLACEMENTPOLICYIfExistsPolicyNamePlacementOptionList
PolicyName
Identifier
PlacementOptionList
PlacementOptionPlacementOptionListPlacementOptionPlacementOptionList,PlacementOption
PlacementOption
CommonPlacementOptionSugarPlacementOptionAdvancedPlacementOption
CommonPlacementOption
FOLLOWERSEqOptLengthNum
SugarPlacementOption
PRIMARY_REGIONEqOptstringLitREGIONSEqOptstringLitSCHEDULEEqOptstringLit
AdvancedPlacementOption
LEARNERSEqOptLengthNumCONSTRAINTSEqOptstringLitLEADER_CONSTRAINTSEqOptstringLitFOLLOWER_CONSTRAINTSEqOptstringLitLEARNER_CONSTRAINTSEqOptstringLitSURVIVAL_PREFERENCESEqOptstringLit

示例

CREATE PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1"; CREATE TABLE t1 (i INT) PLACEMENT POLICY=p1; -- 绑定放置策略 p1 到表 t1。 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。 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。

另请参阅