Add option to disable mongodb cluster status (#7515)

It can be expensive to compute these metrics. In particular, when
retrieveing the amount of jumbo chunks, an index is not being used and
consequently the query triggers an expensive COLLSCAN. For big
databases, this query has negative impact on the cluster performance.

plugins/inputs/mongodb/README.md

@@ -11,6 +11,11 @@
   ##   mongodb://10.10.3.33:18832,
   servers = ["mongodb://127.0.0.1:27017"]
 
+  ## When true, collect cluster status.
+  ## Note that the query that counts jumbo chunks triggers a COLLSCAN, which
+  ## may have an impact on performance.
+  # gather_cluster_status = true
+
   ## When true, collect per database stats
   # gather_perdb_stats = false
 

plugins/inputs/mongodb/mongodb.go

@@ -20,6 +20,7 @@ type MongoDB struct {
 	Servers             []string
 	Ssl                 Ssl
 	mongos              map[string]*Server
+	GatherClusterStatus bool
 	GatherPerdbStats    bool
 	GatherColStats      bool
 	ColStatsDbs         []string
@@ -41,6 +42,11 @@ var sampleConfig = `
   ##   mongodb://10.10.3.33:18832,
   servers = ["mongodb://127.0.0.1:27017"]
 
+  ## When true, collect cluster status
+  ## Note that the query that counts jumbo chunks triggers a COLLSCAN, which
+  ## may have an impact on performance.
+  # gather_cluster_status = true
+
   ## When true, collect per database stats
   # gather_perdb_stats = false
 
@@ -177,14 +183,17 @@ func (m *MongoDB) gatherServer(server *Server, acc telegraf.Accumulator) error {
 		}
 		server.Session = sess
 	}
-	return server.gatherData(acc, m.GatherPerdbStats, m.GatherColStats, m.ColStatsDbs)
+	return server.gatherData(acc, m.GatherClusterStatus, m.GatherPerdbStats, m.GatherColStats, m.ColStatsDbs)
 }
 
 func init() {
 	inputs.Add("mongodb", func() telegraf.Input {
 		return &MongoDB{
-			ColStatsDbs: []string{"local"},
 			mongos:              make(map[string]*Server),
+			GatherClusterStatus: true,
+			GatherPerdbStats:    false,
+			GatherColStats:      false,
+			ColStatsDbs:         []string{"local"},
 		}
 	})
 }

plugins/inputs/mongodb/mongodb_server.go

@@ -192,7 +192,7 @@ func (s *Server) gatherCollectionStats(colStatsDbs []string) (*ColStats, error)
 	return results, nil
 }
 
-func (s *Server) gatherData(acc telegraf.Accumulator, gatherDbStats bool, gatherColStats bool, colStatsDbs []string) error {
+func (s *Server) gatherData(acc telegraf.Accumulator, gatherClusterStatus bool, gatherDbStats bool, gatherColStats bool, colStatsDbs []string) error {
 	s.Session.SetMode(mgo.Eventual, true)
 	s.Session.SetSocketTimeout(0)
 
@@ -218,10 +218,14 @@ func (s *Server) gatherData(acc telegraf.Accumulator, gatherDbStats bool, gather
 		}
 	}
 
-	clusterStatus, err := s.gatherClusterStatus()
+	var clusterStatus *ClusterStatus
+	if gatherClusterStatus {
+		status, err := s.gatherClusterStatus()
 		if err != nil {
 			s.Log.Debugf("Unable to gather cluster status: %s", err.Error())
 		}
+		clusterStatus = status
+	}
 
 	shardStats, err := s.gatherShardConnPoolStats()
 	if err != nil {