planner: Set minimum cost to avoid parent multiplication cost discrepancies (pingcap#56387) (pingcap#56412)

ref pingcap#55126

Author: ti-chi-bot

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

@@ -426,8 +426,8 @@
         "Plan": [
           " TableReader         root         ",
           " └─ExchangeSender    cop[tiflash] ",
-          "   └─Selection       cop[tiflash] gt(test.t1.a, ?)",
-          "     └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.b, ?), 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"
         ]
       },
       {
@@ -443,8 +443,8 @@
         "Plan": [
           " TableReader         root         ",
           " └─ExchangeSender    cop[tiflash] ",
-          "   └─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"
+          "   └─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"
         ]
       },
       {
@@ -461,8 +461,8 @@
         "Plan": [
           " TableReader         root         ",
           " └─ExchangeSender    cop[tiflash] ",
-          "   └─Selection       cop[tiflash] gt(test.t1.b, ?), gt(test.t1.c, ?), or(gt(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, ?), gt(test.t1.c, ?), or(gt(test.t1.a, ?), lt(test.t1.b, ?))",
+          "     └─TableFullScan cop[tiflash] table:t1, range:[?,?], pushed down filter:gt(test.t1.b, ?), keep order:false"
         ]
       },
       {

pkg/planner/core/plan_cost_ver2.go

@@ -798,7 +798,7 @@ func scanCostVer2(option *PlanCostOption, rows, rowSize float64, scanFactor cost
 	}
 	return 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) })
 }
 
@@ -852,7 +852,7 @@ func orderCostVer2(option *PlanCostOption, rows, n float64, byItems []*util.ByIt
 		rows*float64(numFuncs)*cpuFactor.Value,
 		func() string { return fmt.Sprintf("exprCPU(%v*%v*%v)", rows, numFuncs, cpuFactor) })
 	orderCost := 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 sumCostVer2(exprCost, orderCost)
 }

pkg/planner/core/task.go

@@ -310,11 +310,11 @@ func (p *PhysicalIndexJoin) attach2Task(tasks ...task) 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.GetAvgRowSizeListInDisk(stats.HistColl, cols)
+		size = max(cardinality.GetAvgRowSizeListInDisk(stats.HistColl, cols), 0)
 	} else {
 		// Estimate using just the type info.
 		for _, col := range cols {
-			size += float64(chunk.EstimateTypeWidth(col.GetType()))
+			size += max(float64(chunk.EstimateTypeWidth(col.GetType())), 0)
 		}
 	}
 	return