Will Dropped messages gets deleted if addons not configured?

1

Hi,

When I tried to check in HiveMQ control center, i’m able to see a red label with Dropped message (attached screenshot). I don’t know the reason why the messages are getting dropped. In the case of dropped message, will the messages gets deleted when dropped mqtt add-ons topic is not configured ?

If so how to prevent the message being deleted and please provide a solution for this ?

image

2

Hi @Shaku ,
Please provide full page screenshot of your Control Center,
Thanks,
Dasha from HiveMQ team

3

Here is the full page screenshot of HiveMQ control center.

image
image1331×680 62.2 KB

4

Great, @Shaku , can you click on “Dropped messages” on the left side panel?

5

IMG_20220824_172434
IMG_20220824_1724341080×692 66.8 KB

Attached the screenshot that you asked for. We can’t view the dropped messages. Please provide solution for the above questions

6

@Shaku ,
Dropped Message QoS 0 channel not writable means that the publish could not be written on the TCP socket for this client. This could mean that the client did not acknowledge the previous tcp packets (because of a half-open tcp channel for example). Because the publish has QoS-0, the publish is not retried, but dropped (by MQTT specification). Otherwise we would possibly break the requirement of QoS-0 (At-Most-Once).
I suggest you to check your “Clients” list and see which one is subscriber for QoS 0 messages. If your broker sees it as connected, try to disconnect it and let it reconnect.
I hope this helps,
Let me know,
Dasha from HiveMQ team

7

Since i’m new to HiveMQ please clarify this.
the publish has QoS-0, the publish is not retried, but dropped - In the case of dropped message, will the messages gets deleted ? Need more clarification on this.

Thanks

8

Yes, and if you have MQTT Add-Ons enabled, you might observe the message by subscribing to $dropped/#.

For detailed information on dropped messages and the reasons messages are dropped, see Dropped Messages.

I hope this helps,
Dasha from HiveMQ team

9

Then does the below exception occurs because the messages are getting dropped with Qos - 0 channel not writable??

Serialization of kafka metrics failed:
java.lang.IllegalArgumentException: Message size to large. Maximum allowed: 5242880 | Received: 8951417

Also, is there any possibility to fetch the dropped messages back since we need those messages but we have’nt configured Addons.?