opt: add cost penalties and aux flags to log line

All cost penalties and auxiliary flags are now printed in the tracing
log for custom and generic query plan costs. This will aid in debugging.

Release note: None

Author: mgartner

pkg/sql/opt/memo/cost.go

@@ -5,7 +5,11 @@
 
 package memo
 
-import "math"
+import (
+	"fmt"
+	"math"
+	"strings"
+)
 
 // Cost is the best-effort approximation of the actual cost of executing a
 // particular operator tree.
@@ -128,3 +132,37 @@ const (
 	// NoPenalties represents no penalties.
 	NoPenalties Penalties = 0
 )
+
+// Summary returns a short string describing the cost. The format is:
+//
+//	<Cost>:<Penalties>:<aux>
+//
+// Where:
+//
+//	<Cost> is the floating point cost value.
+//	<Penalties> contains "H", "F", or "U" for HugeCostPenalty, FullScanPenalty,
+//	  and UnboundedCardinalityPenalty, respectively.
+//	<aux> contains a number for full scan count and "u" for
+//	  unboundedCardinality.
+//
+// For example, the summary "1.23:HF:5fu" indicates a cost of 1.23 with the
+// HugeCostPenalty and FullScanPenalty penalties, 5 full scans, and the
+// unboundedCardinality flag set.
+func (c Cost) Summary() string {
+	var sb strings.Builder
+	_, _ = fmt.Fprintf(&sb, "%.9g:", c.C)
+	if c.Penalties&HugeCostPenalty != 0 {
+		sb.WriteByte('H')
+	}
+	if c.Penalties&FullScanPenalty != 0 {
+		sb.WriteByte('F')
+	}
+	if c.Penalties&UnboundedCardinalityPenalty != 0 {
+		sb.WriteByte('U')
+	}
+	_, _ = fmt.Fprintf(&sb, ":%df", c.aux.fullScanCount)
+	if c.aux.unboundedCardinality {
+		sb.WriteByte('u')
+	}
+	return sb.String()
+}

pkg/sql/opt/memo/cost_test.go

@@ -70,3 +70,28 @@ func TestCostAdd(t *testing.T) {
 		}
 	}
 }
+
+func TestCostSummary(t *testing.T) {
+	testCases := []struct {
+		c        Cost
+		expected string
+	}{
+		{Cost{C: 1.0}, "1::0f"},
+		{Cost{C: 1.23}, "1.23::0f"},
+		{Cost{C: 1.23456}, "1.23456::0f"},
+		{Cost{C: 1.23, Penalties: HugeCostPenalty}, "1.23:H:0f"},
+		{Cost{C: 1.23, Penalties: FullScanPenalty}, "1.23:F:0f"},
+		{Cost{C: 1.23, Penalties: UnboundedCardinalityPenalty}, "1.23:U:0f"},
+		{Cost{C: 1.23, Penalties: HugeCostPenalty | FullScanPenalty | UnboundedCardinalityPenalty}, "1.23:HFU:0f"},
+		{Cost{C: 1.23, Penalties: HugeCostPenalty | FullScanPenalty | UnboundedCardinalityPenalty}, "1.23:HFU:0f"},
+		{Cost{C: 1.23, aux: testAux{5, false}}, "1.23::5f"},
+		{Cost{C: 1.23, aux: testAux{0, true}}, "1.23::0fu"},
+		{Cost{C: 1.23, aux: testAux{5, true}}, "1.23::5fu"},
+		{Cost{C: 1.23, Penalties: HugeCostPenalty | FullScanPenalty, aux: testAux{5, true}}, "1.23:HF:5fu"},
+	}
+	for _, tc := range testCases {
+		if r := tc.c.Summary(); r != tc.expected {
+			t.Errorf("expected %q, got %q", tc.expected, r)
+		}
+	}
+}

pkg/sql/prep/statement.go

@@ -222,15 +222,14 @@ func (p *planCosts) avgCustom() memo.Cost {
 // Summary returns a single-line string summarizing the custom and generic plan
 // costs and full scan counts. The format for custom costs is:
 //
-//	average_custom_cost [num_custom_costs]{custom_cost_0:full_scan_count ...}
+//	average_custom_cost_float [<count>]{custom_summary_0 custom_summary_1 ...}
 //
-// The format for generic costs is:
-//
-//	generic_cost:generic_full_scan_count
+// The custom costs are follow by the generic cost summary. See
+// (memo.Cost).Summary for details.
 //
 // A full example:
 //
-//	custom costs: 1.23 [3]{1.23:0 1.23:0 1.23:0}, generic cost: 4.56:1
+//	custom costs: 1.5 [3]{1.25:U:0u 1.75:U:0u 1.50:U:0u}, generic cost: 4.56:U:0u
 func (p *planCosts) Summary() string {
 	var sb strings.Builder
 	sb.WriteString("custom costs: ")
@@ -240,15 +239,15 @@ func (p *planCosts) Summary() string {
 			if i > 0 {
 				sb.WriteByte(' ')
 			}
-			sb.WriteString(fmt.Sprintf("%.9g:%d", p.custom.costs[i].C, p.custom.costs[i].FullScanCount()))
+			sb.WriteString(p.custom.costs[i].Summary())
 		}
 		sb.WriteByte('}')
 	} else {
 		sb.WriteString("none")
 	}
 	sb.WriteString(", generic cost: ")
 	if p.HasGeneric() {
-		sb.WriteString(fmt.Sprintf("%.9g:%d", p.generic.C, p.generic.FullScanCount()))
+		sb.WriteString(p.generic.Summary())
 	} else {
 		sb.WriteString("none")
 	}