planner: support explain format='cost_trace' on model ver2

planner/core/cbo_test.go

@@ -57,6 +57,25 @@ func loadTableStats(fileName string, dom *domain.Domain) error {
 	return nil
 }
 
+func TestExplainCostTrace(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t (a int)")
+
+	tk.MustExec("set tidb_cost_model_version=2")
+	tk.MustQuery("explain format='cost_trace' select * from t").Check(testkit.Rows(
+		`TableReader_5 10000.00 177906.67 ((scan(10000*logrowsize(32)*tikv_scan_factor(40.7))) + (net(10000*rowsize(16)*tidb_kv_net_factor(3.96))))/15.00 root  data:TableFullScan_4`,
+		`└─TableFullScan_4 10000.00 2035000.00 scan(10000*logrowsize(32)*tikv_scan_factor(40.7)) cop[tikv] table:t keep order:false, stats:pseudo`))
+
+	tk.MustExec("set tidb_cost_model_version=1")
+	tk.MustQuery("explain format='cost_trace' select * from t").Check(testkit.Rows(
+		// cost trace on model ver1 is not supported
+		`TableReader_5 10000.00 34418.00 N/A root  data:TableFullScan_4`,
+		`└─TableFullScan_4 10000.00 435000.00 N/A cop[tikv] table:t keep order:false, stats:pseudo`,
+	))
+}
+
 func TestExplainAnalyze(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 	tk := testkit.NewTestKit(t, store)

planner/core/common_plans.go

@@ -742,6 +742,8 @@ func (e *Explain) prepareSchema() error {
 		}
 	case format == types.ExplainFormatTrueCardCost:
 		fieldNames = []string{"id", "estRows", "estCost", "costFormula", "actRows", "task", "access object", "execution info", "operator info", "memory", "disk"}
+	case format == types.ExplainFormatCostTrace:
+		fieldNames = []string{"id", "estRows", "estCost", "costFormula", "task", "access object", "operator info"}
 	case (format == types.ExplainFormatROW || format == types.ExplainFormatBrief) && (e.Analyze || e.RuntimeStatsColl != nil):
 		fieldNames = []string{"id", "estRows", "actRows", "task", "access object", "execution info", "operator info", "memory", "disk"}
 	case format == types.ExplainFormatDOT:
@@ -813,8 +815,18 @@ func (e *Explain) RenderResult() error {
 		}
 	}
 
+	if strings.ToLower(e.Format) == types.ExplainFormatCostTrace {
+		if pp, ok := e.TargetPlan.(PhysicalPlan); ok {
+			// record all cost formulas
+			if _, err := getPlanCost(pp, property.RootTaskType,
+				NewDefaultPlanCostOption().WithCostFlag(CostFlagRecalculate|CostFlagTrace)); err != nil {
+				return err
+			}
+		}
+	}
+
 	switch strings.ToLower(e.Format) {
-	case types.ExplainFormatROW, types.ExplainFormatBrief, types.ExplainFormatVerbose, types.ExplainFormatTrueCardCost:
+	case types.ExplainFormatROW, types.ExplainFormatBrief, types.ExplainFormatVerbose, types.ExplainFormatTrueCardCost, types.ExplainFormatCostTrace:
 		if e.Rows == nil || e.Analyze {
 			flat := FlattenPhysicalPlan(e.TargetPlan, true)
 			e.explainFlatPlanInRowFormat(flat)
@@ -1005,9 +1017,13 @@ func (e *Explain) prepareOperatorInfo(p Plan, taskType, id string) {
 		row = append(row, actRows, taskType, accessObject, analyzeInfo, operatorInfo, memoryInfo, diskInfo)
 	} else {
 		row = []string{id, estRows}
-		if strings.ToLower(e.Format) == types.ExplainFormatVerbose || strings.ToLower(e.Format) == types.ExplainFormatTrueCardCost {
+		if strings.ToLower(e.Format) == types.ExplainFormatVerbose || strings.ToLower(e.Format) == types.ExplainFormatTrueCardCost ||
+			strings.ToLower(e.Format) == types.ExplainFormatCostTrace {
 			row = append(row, estCost)
 		}
+		if strings.ToLower(e.Format) == types.ExplainFormatCostTrace {
+			row = append(row, costFormula)
+		}
 		row = append(row, taskType, accessObject, operatorInfo)
 	}
 	e.Rows = append(e.Rows, row)

types/explain_format.go

@@ -35,6 +35,8 @@ var (
 	ExplainFormatBinary = "binary"
 	// ExplainFormatTiDBJSON warp the default result in JSON format
 	ExplainFormatTiDBJSON = "tidb_json"
+	// ExplainFormatCostTrace prints the cost and cost formula of each operator.
+	ExplainFormatCostTrace = "cost_trace"
 
 	// ExplainFormats stores the valid formats for explain statement, used by validator.
 	ExplainFormats = []string{
@@ -48,5 +50,6 @@ var (
 		ExplainFormatTrueCardCost,
 		ExplainFormatBinary,
 		ExplainFormatTiDBJSON,
+		ExplainFormatCostTrace,
 	}
 )