planner: Set minimum cost to avoid parent multiplication cost discrepancies

pkg/planner/core/casetest/testdata/plan_normalized_suite_out.json

@@ -419,17 +419,17 @@
           " TableReader           root         ",
           " └─ExchangeSender      cop[tiflash] ",
           "   └─Projection        cop[tiflash] test.t1.a",
-          "     └─Selection       cop[tiflash] gt(test.t1.b, ?)",
-          "       └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.a, ?), keep order:false"
+          "     └─Selection       cop[tiflash] gt(test.t1.a, ?)",
+          "       └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.b, ?), keep order:false"
         ]
       },
       {
         "SQL": "explain select * from t1 where a>1 and b>1 and c>1",
         "Plan": [
           " TableReader         root         ",
           " └─ExchangeSender    cop[tiflash] ",
-          "   └─Selection       cop[tiflash] gt(test.t1.b, ?)",
-          "     └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.a, ?), gt(test.t1.c, ?), keep order:false"
+          "   └─Selection       cop[tiflash] gt(test.t1.c, ?)",
+          "     └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.a, ?), gt(test.t1.b, ?), keep order:false"
         ]
       },
       {
@@ -445,17 +445,17 @@
         "Plan": [
           " TableReader         root         ",
           " └─ExchangeSender    cop[tiflash] ",
-          "   └─Selection       cop[tiflash] gt(test.t1.b, ?), or(lt(test.t1.a, ?), lt(test.t1.b, ?))",
-          "     └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.a, ?), keep order:false"
+          "   └─Selection       cop[tiflash] gt(test.t1.a, ?), or(lt(test.t1.a, ?), lt(test.t1.b, ?))",
+          "     └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.b, ?), keep order:false"
         ]
       },
       {
         "SQL": "explain select * from t1 where (a<1 or b<2) and (a>3 and b>3) and c>1",
         "Plan": [
           " TableReader         root         ",
           " └─ExchangeSender    cop[tiflash] ",
-          "   └─Selection       cop[tiflash] gt(test.t1.a, ?), gt(test.t1.c, ?), or(lt(test.t1.a, ?), lt(test.t1.b, ?))",
-          "     └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.b, ?), keep order:false"
+          "   └─Selection       cop[tiflash] gt(test.t1.b, ?), gt(test.t1.c, ?), or(lt(test.t1.a, ?), lt(test.t1.b, ?))",
+          "     └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.a, ?), keep order:false"
         ]
       },
       {

pkg/planner/core/plan_cost_ver2.go

@@ -820,7 +820,7 @@ func scanCostVer2(option *optimizetrace.PlanCostOption, rows, rowSize float64, s
 	}
 	return costusage.NewCostVer2(option, scanFactor,
 		// rows * log(row-size) * scanFactor, log2 from experiments
-		rows*math.Log2(rowSize)*scanFactor.Value,
+		rows*max(math.Log2(rowSize), 0)*scanFactor.Value,
 		func() string { return fmt.Sprintf("scan(%v*logrowsize(%v)*%v)", rows, rowSize, scanFactor) })
 }
 
@@ -874,7 +874,7 @@ func orderCostVer2(option *optimizetrace.PlanCostOption, rows, n float64, byItem
 		rows*float64(numFuncs)*cpuFactor.Value,
 		func() string { return fmt.Sprintf("exprCPU(%v*%v*%v)", rows, numFuncs, cpuFactor) })
 	orderCost := costusage.NewCostVer2(option, cpuFactor,
-		rows*math.Log2(n)*cpuFactor.Value,
+		max(rows*math.Log2(n), 0)*cpuFactor.Value,
 		func() string { return fmt.Sprintf("orderCPU(%v*log(%v)*%v)", rows, n, cpuFactor) })
 	return costusage.SumCostVer2(exprCost, orderCost)
 }

pkg/planner/core/task.go

@@ -179,11 +179,11 @@ func (p *PhysicalIndexJoin) Attach2Task(tasks ...base.Task) base.Task {
 // RowSize for cost model ver2 is simplified, always use this function to calculate row size.
 func getAvgRowSize(stats *property.StatsInfo, cols []*expression.Column) (size float64) {
 	if stats.HistColl != nil {
-		size = cardinality.GetAvgRowSizeDataInDiskByRows(stats.HistColl, cols)
+		size = max(cardinality.GetAvgRowSizeDataInDiskByRows(stats.HistColl, cols), 0)
 	} else {
 		// Estimate using just the type info.
 		for _, col := range cols {
-			size += float64(chunk.EstimateTypeWidth(col.GetStaticType()))
+			size += max(float64(chunk.EstimateTypeWidth(col.GetStaticType())), 0)
 		}
 	}
 	return

pkg/planner/util/costusage/cost_misc.go

@@ -59,7 +59,7 @@ type CostVer2 struct {
 
 // GetCost returns the cost value of the costVer2
 func (c *CostVer2) GetCost() float64 {
-	return c.cost
+	return max(c.cost, 0)
 }
 
 // GetTrace returns the trace of current costVer2