add request_count metric to observe the exporter's impact for each sc…

…rape

couchdb-exporter_test.go

@@ -107,7 +107,7 @@ func couchdbResponse(t *testing.T, versionSuffix string) Handler {
 	}
 }
 
-func performCouchdbStatsTest(t *testing.T, couchdbVersion string, expectedMetricsCount int, expectedGetRequestCount float64, expectedDiskSize float64) {
+func performCouchdbStatsTest(t *testing.T, couchdbVersion string, expectedMetricsCount int, expectedGetRequestCount float64, expectedDiskSize float64, expectedRequestCount float64) {
 	basicAuth := lib.BasicAuth{Username: "username", Password: "password"}
 	handler := http.HandlerFunc(BasicAuthHandler(basicAuth, couchdbResponse(t, couchdbVersion)))
 	server := httptest.NewServer(handler)
@@ -148,14 +148,22 @@ func performCouchdbStatsTest(t *testing.T, couchdbVersion string, expectedMetric
 	if expectedDiskSize != actualDiskSize {
 		t.Errorf("expected %f disk size, but got %f instead", expectedDiskSize, actualDiskSize)
 	}
+
+	actualRequestCount, err := testutil.GetGaugeValue(metricFamilies, "couchdb_exporter_request_count", "", "")
+	if err != nil {
+		t.Error(err)
+	}
+	if expectedRequestCount != actualRequestCount {
+		t.Errorf("expected %f request count, but got %f instead", expectedRequestCount, actualRequestCount)
+	}
 }
 
 func TestCouchdbStatsV1(t *testing.T) {
-	performCouchdbStatsTest(t, "v1", 55, 4711, 12396)
+	performCouchdbStatsTest(t, "v1", 56, 4711, 12396, 11)
 }
 
 func TestCouchdbStatsV2(t *testing.T) {
-	performCouchdbStatsTest(t, "v2", 102, 4712, 58570)
+	performCouchdbStatsTest(t, "v2", 103, 4712, 58570, 14)
 }
 
 func TestCouchdbStatsV1Integration(t *testing.T) {

lib/collector.go

@@ -73,6 +73,8 @@ func (e *Exporter) Describe(ch chan<- *prometheus.Desc) {
 	e.activeTasksReplicationLastUpdate.Describe(ch)
 
 	e.viewStaleness.Describe(ch)
+
+	e.requestCount.Describe(ch)
 }
 
 func (e *Exporter) resetAllMetrics() {
@@ -138,6 +140,9 @@ func (e *Exporter) collect(ch chan<- prometheus.Metric) error {
 
 	e.resetAllMetrics()
 
+	e.requestCount.Set(-1)
+	e.client.ResetRequestCount()
+
 	var databases, err = e.getObservedDatabaseNames(e.collectorConfig.Databases)
 	if err != nil {
 		return err
@@ -149,6 +154,7 @@ func (e *Exporter) collect(ch chan<- prometheus.Metric) error {
 		return fmt.Errorf("error collecting couchdb stats: %v", err)
 	}
 	e.up.Set(1)
+	e.requestCount.Set(float64(e.client.GetRequestCount()))
 
 	if stats.ApiVersion == "2" {
 		err = e.collectV2(stats, exposedHttpStatusCodes, e.collectorConfig)
@@ -199,6 +205,8 @@ func (e *Exporter) collect(ch chan<- prometheus.Metric) error {
 
 	e.viewStaleness.Collect(ch)
 
+	e.requestCount.Collect(ch)
+
 	return nil
 }
 

lib/couchdb-client.go

@@ -18,9 +18,11 @@ type BasicAuth struct {
 }
 
 type CouchdbClient struct {
-	BaseUri   string
-	basicAuth BasicAuth
-	client    *http.Client
+	BaseUri           string
+	basicAuth         BasicAuth
+	client            *http.Client
+	ResetRequestCount func()
+	GetRequestCount   func() int
 }
 
 type MembershipResponse struct {
@@ -342,16 +344,38 @@ func (c *CouchdbClient) Request(method string, uri string, body io.Reader) (resp
 	return respData, nil
 }
 
+type requestCountingRoundTripper struct {
+	RequestCount int
+	rt           http.RoundTripper
+}
+
+func (rt *requestCountingRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	rt.RequestCount = rt.RequestCount + 1
+	//glog.Infof("req[%d] %s", rt.RequestCount, req.URL.String())
+	return rt.rt.RoundTrip(req)
+}
+
 func NewCouchdbClient(uri string, basicAuth BasicAuth, insecure bool) *CouchdbClient {
-	httpClient := &http.Client{
-		Transport: &http.Transport{
+	countingRoundTripper := &requestCountingRoundTripper{
+		0,
+		&http.Transport{
 			TLSClientConfig: &tls.Config{InsecureSkipVerify: insecure},
 		},
 	}
 
+	httpClient := &http.Client{
+		Transport: countingRoundTripper,
+	}
+
 	return &CouchdbClient{
 		BaseUri:   uri,
 		basicAuth: basicAuth,
 		client:    httpClient,
+		ResetRequestCount: func() {
+			countingRoundTripper.RequestCount = 0
+		},
+		GetRequestCount: func() int {
+			return countingRoundTripper.RequestCount
+		},
 	}
 }

lib/exporter.go

@@ -14,6 +14,8 @@ type Exporter struct {
 	collectorConfig CollectorConfig
 	mutex           sync.RWMutex
 
+	requestCount prometheus.Gauge
+
 	up             prometheus.Gauge
 	databasesTotal prometheus.Gauge
 	nodeUp         *prometheus.GaugeVec
@@ -59,13 +61,22 @@ func NewExporter(uri string, basicAuth BasicAuth, collectorConfig CollectorConfi
 		client:          NewCouchdbClient(uri, basicAuth, insecure),
 		collectorConfig: collectorConfig,
 
+		requestCount: prometheus.NewGauge(
+			prometheus.GaugeOpts{
+				Namespace: namespace,
+				Subsystem: "exporter",
+				Name:      "request_count",
+				Help:      "Number of CouchDB requests for this scrape.",
+			}),
+
 		up: prometheus.NewGauge(
 			prometheus.GaugeOpts{
 				Namespace: namespace,
 				Subsystem: "httpd",
 				Name:      "up",
 				Help:      "Was the last query of CouchDB stats successful.",
 			}),
+
 		databasesTotal: prometheus.NewGauge(
 			prometheus.GaugeOpts{
 				Namespace: namespace,

testutil/metric-reader.go

@@ -45,6 +45,9 @@ func GetGaugeValue(metricFamilies map[string]*dto.MetricFamily, metricDesc strin
 	for desc, metrics := range metricFamilies {
 		if metricDesc == "" || desc == metricDesc {
 			for _, metric := range metrics.Metric {
+				if len(metric.Label) == 0 && labelName == "" && labelValue == "" {
+					return *metric.Gauge.Value, nil
+				}
 				for _, label := range metric.Label {
 					if *label.Name == labelName && *label.Value == labelValue {
 						return *metric.Gauge.Value, nil