feat(inputs.kafka_consumer): Option to set default fetch message bytes

plugins/inputs/kafka_consumer/README.md

@@ -103,6 +103,13 @@ and use the old zookeeper connection method.
   ## '2 * max_processing_time'.
   # max_processing_time = "100ms"
 
+  ## The default number of message bytes to fetch from the broker in each
+  ## request (default 1MB). This should be larger than the majority of
+  ## your messages, or else the consumer will spend a lot of time
+  ## negotiating sizes and not actually consuming. Similar to the JVM's
+  ## `fetch.message.max.bytes`.
+  # consumer_fetch_default = "1MB"
+
   ## Data format to consume.
   ## Each data format has its own unique set of configuration options, read
   ## more about them here:

plugins/inputs/kafka_consumer/kafka_consumer.go

@@ -43,6 +43,7 @@ type KafkaConsumer struct {
 	BalanceStrategy        string          `toml:"balance_strategy"`
 	Topics                 []string        `toml:"topics"`
 	TopicTag               string          `toml:"topic_tag"`
+	ConsumerFetchDefault   config.Size     `toml:"consumer_fetch_default"`
 
 	kafka.ReadConfig
 
@@ -127,6 +128,10 @@ func (k *KafkaConsumer) Init() error {
 
 	cfg.Consumer.MaxProcessingTime = time.Duration(k.MaxProcessingTime)
 
+	if k.ConsumerFetchDefault != 0 {
+		cfg.Consumer.Fetch.Default = int32(k.ConsumerFetchDefault)
+	}
+
 	k.config = cfg
 	return nil
 }