Add precision rounding to accumulator

Adding precision rounding to the accumulator. This means that now every
input metric will get rounded at collection, rather than at write (and
only for the influxdb output).

This feature is disabled for service inputs, because service inputs
should be in control of their own timestamps & precisions.

plugins/outputs/influxdb/influxdb.go

@@ -24,7 +24,6 @@ type InfluxDB struct {
 	Password         string
 	Database         string
 	UserAgent        string
-	Precision        string
 	RetentionPolicy  string
 	WriteConsistency string
 	Timeout          internal.Duration
@@ -39,6 +38,9 @@ type InfluxDB struct {
 	// Use SSL but skip chain & host verification
 	InsecureSkipVerify bool
 
+	// Precision is only here for legacy support. It will be ignored.
+	Precision string
+
 	conns []client.Client
 }
 
@@ -50,9 +52,6 @@ var sampleConfig = `
   urls = ["http://localhost:8086"] # required
   ## The target database for metrics (telegraf will create it if not exists).
   database = "telegraf" # required
-  ## Precision of writes, valid values are "ns", "us" (or "µs"), "ms", "s", "m", "h".
-  ## note: using "s" precision greatly improves InfluxDB compression.
-  precision = "s"
 
   ## Retention policy to write to.
   retention_policy = "default"
@@ -184,7 +183,6 @@ func (i *InfluxDB) Write(metrics []telegraf.Metric) error {
 	}
 	bp, err := client.NewBatchPoints(client.BatchPointsConfig{
 		Database:         i.Database,
-		Precision:        i.Precision,
 		RetentionPolicy:  i.RetentionPolicy,
 		WriteConsistency: i.WriteConsistency,
 	})