Batch up writes for monitor service

The monitor service was writing one big batch for all stats.  If this
batch was large, it causes some slower and more expensive write paths
to be taken that incur a lot of memory allocations.  This changes the
monitor service to write in batches of up to 5000 points which should
avoid the slower paths.

monitor/service.go

@@ -440,17 +440,26 @@ func (m *Monitor) storeStatistics() {
 				return
 			}
 
-			points := make(models.Points, 0, len(stats))
+			// Write all stats in batches
+			batch := make(models.Points, 0, 5000)
 			for _, s := range stats {
 				pt, err := models.NewPoint(s.Name, models.NewTags(s.Tags), s.Values, now)
 				if err != nil {
 					m.Logger.Info(fmt.Sprintf("Dropping point %v: %v", s.Name, err))
 					return
 				}
-				points = append(points, pt)
+				batch = append(batch, pt)
+				if len(batch) == cap(batch) {
+					m.writePoints(batch)
+					batch = batch[:0]
+
+				}
 			}
 
-			m.writePoints(points)
+			// Write the last batch
+			if len(batch) > 0 {
+				m.writePoints(batch)
+			}
 		case <-m.done:
 			m.Logger.Info(fmt.Sprintf("terminating storage of statistics"))
 			return