Add database connection limits metrics

Signed-off-by: Jocelyn Thode <[email protected]>

Author: jocelynthode

collector/pg_database.go

@@ -53,12 +53,21 @@ var (
 		"Disk space used by the database",
 		[]string{"datname"}, nil,
 	)
+	pgDatabaseConnectionLimitsDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(
+			namespace,
+			databaseSubsystem,
+			"connection_limit",
+		),
+		"Connection limit set for the database",
+		[]string{"datname"}, nil,
+	)
 
-	pgDatabaseQuery     = "SELECT pg_database.datname FROM pg_database;"
+	pgDatabaseQuery     = "select pg_database.datname,pg_database.datconnlimit FROM pg_database"
 	pgDatabaseSizeQuery = "SELECT pg_database_size($1)"
 )
 
-// Update implements Collector and exposes database size.
+// Update implements Collector and exposes database size and connection limits.
 // It is called by the Prometheus registry when collecting metrics.
 // The list of databases is retrieved from pg_database and filtered
 // by the excludeDatabase config parameter. The tradeoff here is that
@@ -81,21 +90,32 @@ func (c PGDatabaseCollector) Update(ctx context.Context, instance *instance, ch
 
 	for rows.Next() {
 		var datname sql.NullString
-		if err := rows.Scan(&datname); err != nil {
+		var connLimit sql.NullInt64
+		if err := rows.Scan(&datname, &connLimit); err != nil {
 			return err
 		}
 
 		if !datname.Valid {
 			continue
 		}
+		database := datname.String
 		// Ignore excluded databases
 		// Filtering is done here instead of in the query to avoid
 		// a complicated NOT IN query with a variable number of parameters
-		if sliceContains(c.excludedDatabases, datname.String) {
+		if sliceContains(c.excludedDatabases, database) {
 			continue
 		}
 
-		databases = append(databases, datname.String)
+		databases = append(databases, database)
+
+		connLimitMetric := 0.0
+		if connLimit.Valid {
+			connLimitMetric = float64(connLimit.Int64)
+		}
+		ch <- prometheus.MustNewConstMetric(
+			pgDatabaseConnectionLimitsDesc,
+			prometheus.GaugeValue, connLimitMetric, database,
+		)
 	}
 
 	// Query the size of the databases
@@ -114,6 +134,7 @@ func (c PGDatabaseCollector) Update(ctx context.Context, instance *instance, ch
 			pgDatabaseSizeDesc,
 			prometheus.GaugeValue, sizeMetric, datname,
 		)
+
 	}
 	return rows.Err()
 }

collector/pg_database_test.go

@@ -31,8 +31,8 @@ func TestPGDatabaseCollector(t *testing.T) {
 
 	inst := &instance{db: db}
 
-	mock.ExpectQuery(sanitizeQuery(pgDatabaseQuery)).WillReturnRows(sqlmock.NewRows([]string{"datname"}).
-		AddRow("postgres"))
+	mock.ExpectQuery(sanitizeQuery(pgDatabaseQuery)).WillReturnRows(sqlmock.NewRows([]string{"datname", "datconnlimit"}).
+		AddRow("postgres", 15))
 
 	mock.ExpectQuery(sanitizeQuery(pgDatabaseSizeQuery)).WithArgs("postgres").WillReturnRows(sqlmock.NewRows([]string{"pg_database_size"}).
 		AddRow(1024))
@@ -47,6 +47,7 @@ func TestPGDatabaseCollector(t *testing.T) {
 	}()
 
 	expected := []MetricResult{
+		{labels: labelMap{"datname": "postgres"}, value: 15, metricType: dto.MetricType_GAUGE},
 		{labels: labelMap{"datname": "postgres"}, value: 1024, metricType: dto.MetricType_GAUGE},
 	}
 	convey.Convey("Metrics comparison", t, func() {
@@ -71,8 +72,8 @@ func TestPGDatabaseCollectorNullMetric(t *testing.T) {
 
 	inst := &instance{db: db}
 
-	mock.ExpectQuery(sanitizeQuery(pgDatabaseQuery)).WillReturnRows(sqlmock.NewRows([]string{"datname"}).
-		AddRow("postgres"))
+	mock.ExpectQuery(sanitizeQuery(pgDatabaseQuery)).WillReturnRows(sqlmock.NewRows([]string{"datname", "datconnlimit"}).
+		AddRow("postgres", nil))
 
 	mock.ExpectQuery(sanitizeQuery(pgDatabaseSizeQuery)).WithArgs("postgres").WillReturnRows(sqlmock.NewRows([]string{"pg_database_size"}).
 		AddRow(nil))
@@ -88,6 +89,7 @@ func TestPGDatabaseCollectorNullMetric(t *testing.T) {
 
 	expected := []MetricResult{
 		{labels: labelMap{"datname": "postgres"}, value: 0, metricType: dto.MetricType_GAUGE},
+		{labels: labelMap{"datname": "postgres"}, value: 0, metricType: dto.MetricType_GAUGE},
 	}
 	convey.Convey("Metrics comparison", t, func() {
 		for _, expect := range expected {