MQTT topics and telegraf.conf

[muibusan]

Hi!

My OpenDTU successfully transmits its MQTT measurements via Telegraf into the the InfluxDB. Voilá.

However, I'm trying to grasp / match the settings in telegraf.conf with the MQTT topics of OpenDTU. It is still confusing me. Can somebody lighten it up please?

According to https://github.com/Setcover/smarthome/blob/main/telegraf/telegraf.conf my telegraf.conf contains the following code:

[[inputs.mqtt_consumer]]
name_override = "OpenDTU"
servers = ["tcp://127.0.0.1:1883"]
#
#   ## Topics that will be subscribed to.
# topics = [ "solar/#" ]
#

  topics = [
    "solar/+/status/+",
    "solar/+/0/+",
    "solar/+/1/+",
    "solar/+/2/+"
  ]
  
  data_format = "value"
  data_type = "float"
  
  tagexclude = ["host","topic"]
  
  [[inputs.mqtt_consumer.topic_parsing]]
    topic = "solar/+/+/+"
    tags = "_/serial/channel/field"
 
 [[processors.pivot]]
  tag_key = "field"
  value_key = "value"

My questions:

1. How to read the topics command? What does the + sign cater for?
2. tagsexlude ... As far as I understand the MQTT documentation there are no topics named "host" and "topic"?! So, does the tagexclude command in the code above make sense? And why exclude "host" and "topic" anyway if the topics-command before only covers "status" and "0/1/2" tags?
3. The topics-command covers input 0,1 and 2. OpenDTU speaks of up to 4 inputs. So, does the topic-command above actually miss input 3?