Log errors when ignoreZeroResult = true (#173)

* Log errors when ignoreZeroResult = true

---------

Signed-off-by: Anders Swanson <anders.swanson@oracle.com>

Author: anders-swanson

collector/collector.go

@@ -360,9 +360,7 @@ func (e *Exporter) scrape(ch chan<- prometheus.Metric, tick *time.Time) {
 					err = err1
 				}
 				errmutex.Unlock()
-				if !metric.IgnoreZeroResult {
-					// do not print repetitive error messages for metrics
-					// with ignoreZeroResult set to true
+				if shouldLogScrapeError(err, metric.IgnoreZeroResult) {
 					level.Error(e.logger).Log("msg", "Error scraping metric",
 						"Context", metric.Context,
 						"MetricsDesc", fmt.Sprint(metric.MetricsDesc),
@@ -622,7 +620,9 @@ func (e *Exporter) scrapeGenericValues(db *sql.DB, ch chan<- prometheus.Metric,
 		return err
 	}
 	if !ignoreZeroResult && metricsCount == 0 {
-		return errors.New("no metrics found while parsing, query returned no rows")
+		// a zero result error is returned for caller error identification.
+		// https://github.com/oracle/oracle-db-appdev-monitoring/issues/168
+		return newZeroResultError()
 	}
 	return err
 }

collector/errors.go

@@ -0,0 +1,25 @@
+// Copyright (c) 2024, Oracle and/or its affiliates.
+// Licensed under the Universal Permissive License v 1.0 as shown at https://oss.oracle.com/licenses/upl.
+
+package collector
+
+import "errors"
+
+type zeroResultError struct {
+	err string
+}
+
+func (z *zeroResultError) Error() string {
+	return z.err
+}
+
+func newZeroResultError() error {
+	return &zeroResultError{
+		err: "no metrics found while parsing, query returned no rows",
+	}
+}
+
+// shouldLogScrapeError returns false if the error is a zero result error and zero result errors are ignored.
+func shouldLogScrapeError(err error, isIgnoreZeroResult bool) bool {
+	return !isIgnoreZeroResult || !errors.Is(err, newZeroResultError())
+}