Re: [mosquitto-dev] Question about persistent session behavior after bro

["c@xxxxxxxx" <c@xxxxxxxx>]

Hi Mohd,

did you specify Qos = 1 in the subscribing client?

did you specify clean_session false on the second connect of the subscriber?

If you do so, messages published before and after the restart of mosquitto are delivered:

```

$ mosquitto_sub -t persist -i sub -c -q 1

^C

$ mosquitto_pub -t 'persist' -i pub -q 1 -m one

$ mosquitto_pub -t 'persist' -i pub -q 1 -m two

$ mosquitto_pub -t 'persist' -i pub -q 1 -m three

*** restart mosquitto *** 

$ mosquitto_pub -t 'persist' -i pub -q 1 -m four

$ mosquitto_pub -t 'persist' -i pub -q 1 -m five

$ mosquitto_pub -t 'persist' -i pub -q 1 -m six

$ mosquitto_sub -t persist -i sub -c -q 1

one

two

three

four

five

six

```

If your situation is different, show us the mosquitto.log file.

Cheers

   Christoph

Am 08.10.2025 um 01:22 schrieb uvaish siddiqui via mosquitto-dev <mosquitto-dev@xxxxxxxxxxx>:

Hello Mosquitto Developers,

I’ve observed a behavior with persistent sessions in Mosquitto and would like to confirm if this is expected.

Setup:

Mosquitto version 2.0.22 with persistence enabled:

persistence true

persistence_location /path/mosq/data/

MQTT v3.1.1 clients using stable client_ids.

Publisher uses QoS 1.

Subscriber (client2) connects with clean_session=false and then disconnects.

Test sequence:

1. Both publisher and subscriber connect. Subscriber uses clean_session=false.

2. Disconnect client2 and keep it offline.

3. Publish some X messages → they queue for client2.

4. Restart the Mosquitto broker (so it reloads its persistent database).

5. Without reconnecting client2, publish some more Y messages.

6. Reconnect client2.

Result:

On reconnect, client2 receives the X messages (published before the broker restart).

It does not receive the Y messages published after the restart while it was still offline.

Question:

Is this the intended behavior?

After a broker restart, must a client reconnect at least once to re-establish its session before the broker will queue new QoS 1 messages for it?

I had assumed that if a session was persisted and restored, the broker would continue to queue new QoS 1 messages for that client even if it hadn’t reconnected yet — but in my test, that did not happen.

Thanks for clarifying how persistent sessions are expected to behave after a restart.

Regards,

Mohd Uvaish

New Delhi, India

uvaishbharat@xxxxxxxxx 

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