ALTER PLACEMENT POLICY

ALTER PLACEMENT POLICY is used to modify existing placement policies that have previously been created. All the tables and partitions which use the placement policy will automatically be updated.

ALTER PLACEMENT POLICY replaces the previous policy with the new definition. It does not merge the old policy with the new one. In the following example, FOLLOWERS=4 is lost when the ALTER PLACEMENT POLICY is executed:

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

Synopsis

AlterPolicyStmt ::=
    "ALTER" "PLACEMENT" "POLICY" IfExists PolicyName PlacementOptionList

PolicyName ::=
    Identifier

PlacementOptionList ::=
    PlacementOption
|   PlacementOptionList PlacementOption
|   PlacementOptionList ',' PlacementOption

PlacementOption ::=
    CommonPlacementOption
|   SugarPlacementOption
|   AdvancedPlacementOption

CommonPlacementOption ::=
    "FOLLOWERS" EqOpt LengthNum

SugarPlacementOption ::=
    "PRIMARY_REGION" EqOpt stringLit
|   "REGIONS" EqOpt stringLit
|   "SCHEDULE" EqOpt stringLit

AdvancedPlacementOption ::=
    "LEARNERS" EqOpt LengthNum
|   "CONSTRAINTS" EqOpt stringLit
|   "LEADER_CONSTRAINTS" EqOpt stringLit
|   "FOLLOWER_CONSTRAINTS" EqOpt stringLit
|   "LEARNER_CONSTRAINTS" EqOpt stringLit

Examples

CREATE PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1";
CREATE TABLE t1 (i INT) PLACEMENT POLICY=p1; -- Assign policy p1 to table t1
ALTER PLACEMENT POLICY p1 PRIMARY_REGION="us-east-1" REGIONS="us-east-1,us-west-1,us-west-2" FOLLOWERS=4; -- The rules of t1 will be updated automatically.
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 compatibility

This statement is a TiDB extension to MySQL syntax.

See also

• Placement Rules in SQL
• SHOW PLACEMENT
• CREATE PLACEMENT POLICY
• DROP PLACEMENT POLICY