feat(bigquery): add reservation usage stats to query statistics (#3403)

* feat: add reservation usage stats to query statistics

This PR plumbs through reservation usage stats reported per-job.

Also added a small integration test for testing query statistics,
as we didn't have one previously.

Author: shollyman

Diff for: bigquery/integration_test.go

@@ -1630,6 +1630,63 @@ func TestIntegration_TableUpdate(t *testing.T) {
 	}
 }
 
+func TestIntegration_QueryStatistics(t *testing.T) {
+	// Make a bunch of assertions on a simple query.
+	if client == nil {
+		t.Skip("Integration tests skipped")
+	}
+	ctx := context.Background()
+
+	q := client.Query("SELECT 17 as foo, 3.14 as bar")
+	// disable cache to ensure we have query statistics
+	q.DisableQueryCache = true
+
+	job, err := q.Run(ctx)
+	if err != nil {
+		t.Fatalf("job Run failure: %v", err)
+	}
+	status, err := job.Wait(ctx)
+	if err != nil {
+		t.Fatalf("job Wait failure: %v", err)
+	}
+	if status.Statistics == nil {
+		t.Fatal("expected job statistics, none found")
+	}
+
+	if status.Statistics.NumChildJobs != 0 {
+		t.Errorf("expected no children, %d reported", status.Statistics.NumChildJobs)
+	}
+
+	if status.Statistics.ParentJobID != "" {
+		t.Errorf("expected no parent, but parent present: %s", status.Statistics.ParentJobID)
+	}
+
+	if status.Statistics.Details == nil {
+		t.Fatal("expected job details, none present")
+	}
+
+	qStats, ok := status.Statistics.Details.(*QueryStatistics)
+	if !ok {
+		t.Fatalf("expected query statistics not present")
+	}
+
+	if qStats.CacheHit {
+		t.Error("unexpected cache hit")
+	}
+
+	if qStats.StatementType != "SELECT" {
+		t.Errorf("expected SELECT statement type, got: %s", qStats.StatementType)
+	}
+
+	if len(qStats.QueryPlan) == 0 {
+		t.Error("expected query plan, none present")
+	}
+
+	if len(qStats.Timeline) == 0 {
+		t.Error("expected query timeline, none present")
+	}
+}
+
 func TestIntegration_Load(t *testing.T) {
 	if client == nil {
 		t.Skip("Integration tests skipped")

Diff for: bigquery/job.go

@@ -347,6 +347,9 @@ type JobStatistics struct {
 	// ScriptStatistics includes information run as part of a child job within
 	// a script.
 	ScriptStatistics *ScriptStatistics
+
+	// ReservationUsage attributes slot consumption to reservations.
+	ReservationUsage []*ReservationUsage
 }
 
 // Statistics is one of ExtractStatistics, LoadStatistics or QueryStatistics.
@@ -561,6 +564,25 @@ type QueryTimelineSample struct {
 	SlotMillis int64
 }
 
+// ReservationUsage contains information about a job's usage of a single reservation.
+type ReservationUsage struct {
+	// SlotMillis reports the slot milliseconds utilized within in the given reservation.
+	SlotMillis int64
+	// Name indicates the utilized reservation name, or "unreserved" for ondemand usage.
+	Name string
+}
+
+func bqToReservationUsage(ru []*bq.JobStatisticsReservationUsage) []*ReservationUsage {
+	var usage []*ReservationUsage
+	for _, in := range ru {
+		usage = append(usage, &ReservationUsage{
+			SlotMillis: in.SlotMs,
+			Name:       in.Name,
+		})
+	}
+	return usage
+}
+
 // ScriptStatistics report information about script-based query jobs.
 type ScriptStatistics struct {
 	EvaluationKind string
@@ -810,6 +832,7 @@ func (j *Job) setStatistics(s *bq.JobStatistics, c *Client) {
 		NumChildJobs:        s.NumChildJobs,
 		ParentJobID:         s.ParentJobId,
 		ScriptStatistics:    bqToScriptStatistics(s.ScriptStatistics),
+		ReservationUsage:    bqToReservationUsage(s.ReservationUsage),
 	}
 	switch {
 	case s.Extract != nil: