# MQTT - parsing / topic problem **URL:** \ **Category:** Telegraf\ **Tags:** mqtt\ **Created:** [March 14, 2023, 6:01pm UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061 "2023-03-14T18:01:59Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Heinz](https://avatars.discourse-cdn.com/v4/letter/h/f04885/32.png) [@Heinz](https://community.influxdata.com/u/Heinz)\ **Post date:** [March 14, 2023, 6:01pm UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061/1 "2023-03-14T18:01:59Z")
i am reading data from a microcontroller home/room/workshop/temperature1 20.36 home/room/workshop/humidity 46.36 home/room/workshop/pressure 996.27 home/room/workshop/temperature2 16.94 i read in this data with telegraf telegraf.conf … [[inputs.mqtt\_consumer]] … topics = [ “home/+/+/+”, ] … data\_format = “value” data\_type = “float” and [[inputs.mqtt\_consumer.topic\_parsing]] topic = “home/+/+/+” measurement = “measurement/_/_/_" tags = "_/location1/location2/field” #fields = “_/_/\_/test” # ## Value supported is int, float, unit # # [[inputs.mqtt\_consumer.topic.types]] # key = float [[processors.pivot]] tag\_key = “field” value\_key = “value” output from the log file home,location1=room,location2=workshop,topic=home/room/workshop/temperature2 temperature2=16.88 1678815798606918574 my problem is now, the issue of topic=.. since this is also written to the database A solution is to leave out the topic area [[inputs.mqtt\_consumer.topic\_parsing]], but then telegraf no longer starts. 2023-03-14T17:53:25Z E! [telegraf] Error running agent: could not initialize input inputs.mqtt\_consumer: config error topic parsing: measurement length does not equal topic length the database entry Table: keys: [\_start, \_stop, \_field, \_measurement, location1, location2, topic] \_start:time \_stop:time \_field:string \_measurement:string location1:string location2:string topic:string \_time:time \_value:float * * * 2023-03-14T17:27:59.732326779Z 2023-03-14T17:57:59.732326779Z temperature1 home room workshop home/room/workshop/temperature1 2023-03-14T17:31:18.550720212Z 20.19 I don’t know how I don’t get this entry topic= transferred to the database Tanks ---
**Author:** ![srebhan](https://sea1.discourse-cdn.com/flex023/user_avatar/community.influxdata.com/srebhan/32/8572_2.png) [@srebhan](https://community.influxdata.com/u/srebhan)\ **Post date:** [March 15, 2023, 11:25am UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061/2 "2023-03-15T11:25:12Z")
Your topic parsing section is screwed… Every element there has to have the same (topic-length) number of elements e.g. ```toml [[inputs.mqtt_consumer.topic_parsing]] topic = "home/+/+/+" measurement = "/measurement/_/_/_" tags = "/_/location1/location2/field" ``` ---
**Author:** ![Heinz](https://avatars.discourse-cdn.com/v4/letter/h/f04885/32.png) [@Heinz](https://community.influxdata.com/u/Heinz)\ **Post date:** [March 15, 2023, 1:31pm UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061/3 "2023-03-15T13:31:29Z")
Hi, I don’t understand the hint. My topic from controller is: home/room/workshop/temperature1 23.02 home/room/workshop/humidity 37.63 home/room/workshop/pressure 1012.33 home/room/workshop/temperature2 19.06 I have four entries home measurement room location1 workshop location2 temperature1 field [[inputs.mqtt\_consumer.topic\_parsing]] topic = “home/+/+/+” measurement = “measurement/_/_/_" tags = "_/location1/location2/field” #fields = “_/_/\_/field” The entry in the database is: Table: keys: [\_start, \_stop, \_field, \_measurement, location1, location2, topic] \_start:time \_stop:time \_field:string \_measurement:string location1:string location2:string **topic:string** \_time:time \_value:float * * * 2023-03-15T13:15:07.861256140Z 2023-03-15T13:25:07.861256140Z temperature2 home room workshop **home/room/workshop/temperature2** 2023-03-15T13:24:48.356193692Z 19.31 It doesn’t look bad, but the **topic** entry shouldn’t be there. I can’t get rid of this entry with telegraf. ---
**Author:** ![Heinz](https://avatars.discourse-cdn.com/v4/letter/h/f04885/32.png) [@Heinz](https://community.influxdata.com/u/Heinz)\ **Post date:** [March 17, 2023, 4:58pm UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061/4 "2023-03-17T16:58:21Z")
I tested a little. The configuration works fine, but the “topic” entry in the database doesn’t have to be. [[inputs.mqtt\_consumer.topic\_parsing]] topic = “home/+/+/+” measurement = “measurement/_/_/_" tags = "_/location1/location2/field” #fields = “_/_/\_/field” [[processors.pivot]] tag\_key = “field” value\_key = “value” It just takes up space. If someone else has an idea, that would be nice, otherwise I’ll write a program. 2023-03-17T16:40:57.273213356Z 2023-03-17T16:50:57.273213356Z temperature2 home room workshop **home/room/workshop/temperature2** 2023-03-17T16:50:32.177384182Z 19.31 Note: the description “MQTT Consumer Telegraf Input Plugin” does not work > **[MQTT Consumer Telegraf Input Plugin | InfluxData](https://www.influxdata.com/integration/mqtt-telegraf-consumer/)** > > InfluxData Integrations: Learn how to consume MQTT messages using Telegraf. example … [[inputs.mqtt\_consumer]] … topics = “/sensors/#” [[inputs.mqtt\_consumer.topic\_parsing]] measurement = “/measurement/_/_/_/_” tags = “/\_/site/version/device\_name/field” [[processors.pivot]] tag\_key = “field” value\_key = “value” greetings ---
**Author:** ![srebhan](https://sea1.discourse-cdn.com/flex023/user_avatar/community.influxdata.com/srebhan/32/8572_2.png) [@srebhan](https://community.influxdata.com/u/srebhan)\ **Post date:** [March 21, 2023, 9:39am UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061/5 "2023-03-21T09:39:24Z")
@Heinz the topic takes up exactly **one time** the byte size of the topic text for InfluxDB, but you can get rid of it using [metric modifiers](https://github.com/influxdata/telegraf/blob/master/docs/CONFIGURATION.md#modifiers) more specifically `tagexclude`. ---
**Author:** ![Heinz](https://avatars.discourse-cdn.com/v4/letter/h/f04885/32.png) [@Heinz](https://community.influxdata.com/u/Heinz)\ **Post date:** [April 6, 2023, 4:14pm UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061/6 "2023-04-06T16:14:56Z")
Thanks for the info. I wasn’t at home and will try it now. ---
**Author:** ![Heinz](https://avatars.discourse-cdn.com/v4/letter/h/f04885/32.png) [@Heinz](https://community.influxdata.com/u/Heinz)\ **Post date:** [April 12, 2023, 8:40am UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061/7 "2023-04-12T08:40:06Z")
Hello, i have some problems with the syntax. tagexclude = [“home”] doesn’t work that way my solution is: [[inputs.mqtt\_consumer]] … ## Topics that will be subscribed to. ``` topics = [ "home/#" ] ``` … data\_format = “value” data\_type = “float” topic\_tag = “” now the topic is no longer stored in the database. \_start:time \_stop:time \_field:string \_measurement:string location1:string location2:string \_time:time \_value:float * * * 2023-04-12T08:27:32.087611861Z temperature2 home room workshop 2023-04-12T08:28:11.393511938Z 10.69 2023-04-12T08:27:32.087611861Z temperature2 home room workshop 2023-04-12T08:29:11.396965350Z 10.75 I don’t know if it’s the best solution, but this is how it works ---
**Author:** ![srebhan](https://sea1.discourse-cdn.com/flex023/user_avatar/community.influxdata.com/srebhan/32/8572_2.png) [@srebhan](https://community.influxdata.com/u/srebhan)\ **Post date:** [May 16, 2023, 2:30pm UTC](https://community.influxdata.com/t/mqtt-parsing-topic-problem/29061/8 "2023-05-16T14:30:21Z")
Well it would be `tagexclude = ["topic"]` as the tag is named `topic`…