fix issue prometheus-community#358: descriptors reported by collector have inconsistent label names

Signed-off-by: zhoujk <[email protected]>

Author: quenlang

cmd/postgres_exporter/pg_setting.go

@@ -18,11 +18,17 @@ import (
 	"math"
 	"strconv"
 	"strings"
+	"sync"
 
 	"github.com/go-kit/kit/log/level"
 	"github.com/prometheus/client_golang/prometheus"
 )
 
+var (
+	// cache the first server setting when there are multiple servers
+	shortDescCache sync.Map
+)
+
 // Query the pg_settings view containing runtime variables
 func querySettings(ch chan<- prometheus.Metric, server *Server) error {
 	level.Debug(logger).Log("msg", "Querying pg_setting view", "server", server)
@@ -46,6 +52,15 @@ func querySettings(ch chan<- prometheus.Metric, server *Server) error {
 			return fmt.Errorf("Error retrieving rows on %q: %s %v", server, namespace, err)
 		}
 
+		// once the first server setting shortDesc cached, the other server re-use the first cache
+		if v, ok := shortDescCache.Load(s.name); !ok {
+			shortDescCache.Store(s.name, s.shortDesc)
+		} else {
+			if shortDesc, ok := v.(string); ok {
+				s.shortDesc = shortDesc
+			}
+		}
+
 		ch <- s.metric(server.labels)
 	}