Revert "GODRIVER-2626 further optimize selectByKind for special case of all fitting servers (#1107)"

This reverts commit dd15cfb.

Author: prestonvasquez

mongo/description/selector_test.go

@@ -300,69 +300,32 @@ func BenchmarkLatencySelector(b *testing.B) {
 }
 
 func BenchmarkSelector_Sharded(b *testing.B) {
-	for _, bcase := range []struct {
-		name        string
-		serversHook func(servers []Server)
-	}{
-		{
-			name:        "AllFit",
-			serversHook: func(servers []Server) {},
-		},
-		{
-			name: "AllButOneFit",
-			serversHook: func(servers []Server) {
-				servers[0].Kind = LoadBalancer
-			},
-		},
-		{
-			name: "HalfFit",
-			serversHook: func(servers []Server) {
-				for i := 0; i < len(servers); i += 2 {
-					servers[i].Kind = LoadBalancer
-				}
-			},
-		},
-		{
-			name: "OneFit",
-			serversHook: func(servers []Server) {
-				for i := 1; i < len(servers); i++ {
-					servers[i].Kind = LoadBalancer
-				}
-			},
-		},
-	} {
-		bcase := bcase
-
-		b.Run(bcase.name, func(b *testing.B) {
-			subject := readpref.Primary()
-
-			s := Server{
-				Addr:              address.Address("localhost:27017"),
-				HeartbeatInterval: time.Duration(10) * time.Second,
-				LastWriteTime:     time.Date(2017, 2, 11, 14, 0, 0, 0, time.UTC),
-				LastUpdateTime:    time.Date(2017, 2, 11, 14, 0, 2, 0, time.UTC),
-				Kind:              Mongos,
-				WireVersion:       &VersionRange{Min: 0, Max: 5},
-			}
-			servers := make([]Server, 100)
-			for i := 0; i < len(servers); i++ {
-				servers[i] = s
-			}
-			bcase.serversHook(servers)
-			c := Topology{
-				Kind:    Sharded,
-				Servers: servers,
-			}
+	subject := readpref.Primary()
 
-			b.ResetTimer()
-			b.RunParallel(func(p *testing.PB) {
-				b.ReportAllocs()
-				for p.Next() {
-					_, _ = ReadPrefSelector(subject).SelectServer(c, c.Servers)
-				}
-			})
-		})
+	s := Server{
+		Addr:              address.Address("localhost:27017"),
+		HeartbeatInterval: time.Duration(10) * time.Second,
+		LastWriteTime:     time.Date(2017, 2, 11, 14, 0, 0, 0, time.UTC),
+		LastUpdateTime:    time.Date(2017, 2, 11, 14, 0, 2, 0, time.UTC),
+		Kind:              Mongos,
+		WireVersion:       &VersionRange{Min: 0, Max: 5},
+	}
+	servers := make([]Server, 100)
+	for i := 0; i < len(servers); i++ {
+		servers[i] = s
+	}
+	servers[0].Kind = LoadBalancer
+	c := Topology{
+		Kind:    Sharded,
+		Servers: servers,
 	}
+
+	b.ResetTimer()
+	b.RunParallel(func(p *testing.PB) {
+		for p.Next() {
+			_, _ = ReadPrefSelector(subject).SelectServer(c, c.Servers)
+		}
+	})
 }
 
 func TestSelector_Single(t *testing.T) {

mongo/description/server_selector.go

@@ -310,9 +310,6 @@ func selectByKind(candidates []Server, kind ServerKind) []Server {
 			viableIndexes = append(viableIndexes, i)
 		}
 	}
-	if len(viableIndexes) == len(candidates) {
-		return candidates
-	}
 	result := make([]Server, len(viableIndexes))
 	for i, idx := range viableIndexes {
 		result[i] = candidates[idx]