Remove outputs blocking inputs when output is slow (#4938)

plugins/processors/topk/topk.go

@@ -10,6 +10,7 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/filter"
 	"github.com/influxdata/telegraf/internal"
+	"github.com/influxdata/telegraf/metric"
 	"github.com/influxdata/telegraf/plugins/processors"
 )
 
@@ -76,12 +77,12 @@ var sampleConfig = `
   ## tags. If this setting is different than "" the plugin will add a
   ## tag (which name will be the value of this setting) to each metric with
   ## the value of the calculated GroupBy tag. Useful for debugging
-  # add_groupby_tag = ""          
+  # add_groupby_tag = ""
 
   ## These settings provide a way to know the position of each metric in
   ## the top k. The 'add_rank_field' setting allows to specify for which
   ## fields the position is required. If the list is non empty, then a field
-  ## will be added to each and every metric for each string present in this 
+  ## will be added to each and every metric for each string present in this
   ## setting. This field will contain the ranking of the group that
   ## the metric belonged to when aggregated over that field.
   ## The name of the field will be set to the name of the aggregation field,
@@ -208,6 +209,11 @@ func (t *TopK) Apply(in ...telegraf.Metric) []telegraf.Metric {
 
 	// Add the metrics received to our internal cache
 	for _, m := range in {
+		// When tracking metrics this plugin could deadlock the input by
+		// holding undelivered metrics while the input waits for metrics to be
+		// delivered.  Instead, treat all handled metrics as delivered and
+		// produced metrics as untracked in a similar way to aggregators.
+		m.Drop()
 
 		// Check if the metric has any of the fields over which we are aggregating
 		hasField := false
@@ -281,7 +287,6 @@ func (t *TopK) push() []telegraf.Metric {
 
 		// Create a one dimensional list with the top K metrics of each key
 		for i, ag := range aggregations[0:min(t.K, len(aggregations))] {
-
 			// Check whether of not we need to add fields of tags to the selected metrics
 			if len(t.aggFieldSet) != 0 || len(t.rankFieldSet) != 0 || groupTag != "" {
 				for _, m := range t.cache[ag.groupbykey] {
@@ -311,7 +316,16 @@ func (t *TopK) push() []telegraf.Metric {
 
 	t.Reset()
 
-	return ret
+	result := make([]telegraf.Metric, 0, len(ret))
+	for _, m := range ret {
+		copy, err := metric.New(m.Name(), m.Tags(), m.Fields(), m.Time(), m.Type())
+		if err != nil {
+			continue
+		}
+		result = append(result, copy)
+	}
+
+	return result
 }
 
 // Function that generates the aggregation functions

plugins/processors/topk/topk_test.go

@@ -1,12 +1,12 @@
 package topk
 
 import (
-	"reflect"
 	"testing"
 	"time"
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
+	"github.com/influxdata/telegraf/testutil"
 )
 
 // Key, value pair that represents a telegraf.Metric Field
@@ -95,7 +95,7 @@ func deepCopy(a []telegraf.Metric) []telegraf.Metric {
 
 func belongs(m telegraf.Metric, ms []telegraf.Metric) bool {
 	for _, i := range ms {
-		if reflect.DeepEqual(i, m) {
+		if testutil.MetricEqual(i, m) {
 			return true
 		}
 	}