Fix issue where empty metrics could be returned

The scraper was pre-initializing metrics, and would
return them regardless of whether or not any data points
were actually collected. This resulted in empty metrics
being returned.

CHANGELOG.md

@@ -20,7 +20,7 @@
 ## 🧰 Bug fixes 🧰
 
 - `resourcedetectionprocessor`: fix `meta` allow list excluding keys with nil values (#7424)
-
+- `postgresqlreceiver`: Fix issue where empty metrics could be returned after failed connection (#7502)
 ## v0.43.0
 
 ## 💡 Enhancements 💡

receiver/postgresqlreceiver/scraper.go

@@ -79,6 +79,23 @@ func addToIntMetric(metric pdata.NumberDataPointSlice, attributes pdata.Attribut
 
 // scrape scrapes the metric stats, transforms them and attributes them into a metric slices.
 func (p *postgreSQLScraper) scrape(ctx context.Context) (pdata.Metrics, error) {
+	databases := p.config.Databases
+	listClient, err := p.clientFactory.getClient(p.config, "")
+	if err != nil {
+		p.logger.Error("Failed to initialize connection to postgres", zap.Error(err))
+		return pdata.NewMetrics(), err
+	}
+	defer listClient.Close()
+
+	if len(databases) == 0 {
+		dbList, err := listClient.listDatabases(ctx)
+		if err != nil {
+			p.logger.Error("Failed to request list of databases from postgres", zap.Error(err))
+			return pdata.NewMetrics(), err
+		}
+		databases = dbList
+	}
+
 	// metric initialization
 	md := pdata.NewMetrics()
 	ilm := md.ResourceMetrics().AppendEmpty().InstrumentationLibraryMetrics().AppendEmpty()
@@ -95,26 +112,6 @@ func (p *postgreSQLScraper) scrape(ctx context.Context) (pdata.Metrics, error) {
 
 	var errors scrapererror.ScrapeErrors
 
-	databases := p.config.Databases
-	listClient, err := p.clientFactory.getClient(p.config, "")
-	if err != nil {
-		p.logger.Error("Failed to initialize connection to postgres", zap.Error(err))
-		errors.Add(err)
-		return md, errors.Combine()
-	}
-	defer listClient.Close()
-
-	if len(databases) == 0 {
-		dbList, err := listClient.listDatabases(ctx)
-		if err != nil {
-			p.logger.Error("Failed to request list of databases from postgres", zap.Error(err))
-			errors.Add(err)
-			return md, errors.Combine()
-		}
-
-		databases = dbList
-	}
-
 	p.collectCommitsAndRollbacks(ctx, now, listClient, databases, commits, rollbacks, errors)
 	p.collectDatabaseSize(ctx, now, listClient, databases, databaseSize, errors)
 	p.collectBackends(ctx, now, listClient, databases, backends, errors)
@@ -132,6 +129,9 @@ func (p *postgreSQLScraper) scrape(ctx context.Context) (pdata.Metrics, error) {
 		p.collectDatabaseTableMetrics(ctx, now, dbClient, databaseRows, operations, errors)
 	}
 
+	if md.DataPointCount() == 0 {
+		md = pdata.NewMetrics()
+	}
 	return md, errors.Combine()
 }
 

receiver/postgresqlreceiver/scraper_test.go

@@ -22,12 +22,25 @@ import (
 
 	"github.com/stretchr/testify/mock"
 	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/collector/model/pdata"
 	"go.uber.org/zap"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/scrapertest"
 	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/scrapertest/golden"
 )
 
+func TestUnsuccessfulScrape(t *testing.T) {
+	factory := NewFactory()
+	cfg := factory.CreateDefaultConfig().(*Config)
+	cfg.Endpoint = "fake:11111"
+
+	scraper := newPostgreSQLScraper(zap.NewNop(), cfg, &defaultClientFactory{})
+	actualMetrics, err := scraper.scrape(context.Background())
+	require.Error(t, err)
+
+	require.NoError(t, scrapertest.CompareMetrics(pdata.NewMetrics(), actualMetrics))
+}
+
 func TestScraper(t *testing.T) {
 	factory := new(mockClientFactory)
 	factory.initMocks([]string{"otel"})