Remove system colections from index stats (#893)

Author: ramunas-omnisend

exporter/indexstats_collector.go

@@ -94,6 +94,11 @@ func (d *indexstatsCollector) collect(ch chan<- prometheus.Metric) {
 		database := parts[0]
 		collection := strings.Join(parts[1:], ".")
 
+		// exclude system collections
+		if strings.HasPrefix(collection, "system.") {
+			continue
+		}
+
 		aggregation := bson.D{
 			{Key: "$indexStats", Value: bson.M{}},
 		}