planner: fix the wrong cost formula of MPPExchanger on cost model ver2 (

#35718) ref #35240
pingcap · Jun 27, 2022 · ab27d49 · ab27d49
1 parent 31c92c6
commit ab27d49
Showing 1 changed file with 6 additions and 2 deletions.
diff --git a/planner/core/plan_cost.go b/planner/core/plan_cost.go
@@ -1209,8 +1209,12 @@ func (p *PhysicalExchangeReceiver) GetPlanCost(taskType property.TaskType, costF
 	}
 	p.planCost = childCost
 	// accumulate net cost
-	// TODO: this formula is wrong since it doesn't consider tableRowSize, fix it later
-	p.planCost += getCardinality(p.children[0], costFlag) * p.ctx.GetSessionVars().GetNetworkFactor(nil)
+	if p.ctx.GetSessionVars().CostModelVersion == modelVer1 {
+		p.planCost += getCardinality(p.children[0], costFlag) * p.ctx.GetSessionVars().GetNetworkFactor(nil)
+	} else { // to avoid regression, only consider row-size on model ver2
+		rowSize := getTblStats(p.children[0]).GetAvgRowSize(p.ctx, p.children[0].Schema().Columns, false, false)
+		p.planCost += getCardinality(p.children[0], costFlag) * rowSize * p.ctx.GetSessionVars().GetNetworkFactor(nil)
+	}
 	p.planCostInit = true
 	return p.planCost, nil
 }