add param use_even_strategy

plugin/task_manager/cluster_migration/cluster_migration.go

@@ -209,6 +209,7 @@ func (p *processor) splitMajorMigrationTask(taskItem *task.Task) error {
 				FieldName: index.Partition.FieldName,
 				FieldType: index.Partition.FieldType,
 				Step:      index.Partition.Step,
+				UseEvenStrategy: index.Partition.UseEvenStrategy,
 			}
 			if source.QueryDSL != nil {
 				partitionQ.Filter = source.QueryDSL

plugin/task_manager/model/common.go

@@ -36,6 +36,8 @@ type IndexPartition struct {
 	FieldType string      `json:"field_type"`
 	FieldName string      `json:"field_name"`
 	Step      interface{} `json:"step"`
+	//only worked when field type equals number
+	UseEvenStrategy bool `json:"use_even_strategy"`
 }
 
 type IndexIncremental struct {