Github user JPercivall commented on a diff in the pull request:
https://github.com/apache/nifi/pull/548#discussion_r67948120
--- Diff:
nifi-nar-bundles/nifi-mqtt-bundle/nifi-mqtt-processors/src/main/java/org/apache/nifi/processors/mqtt/ConsumeMQTT.java
---
@@ -289,8 +296,10 @@ public void process(final OutputStream out) throws
IOException {
String transitUri = new
StringBuilder(broker).append(mqttMessage.getTopic()).toString();
session.getProvenanceReporter().receive(messageFlowfile,
transitUri);
session.transfer(messageFlowfile, REL_MESSAGE);
- mqttQueue.remove(mqttMessage);
session.commit();
+ if (!mqttQueue.remove(mqttMessage)) {
+ logger.warn("Mqtt message " + mqttMessage + " had already
been removed from queue, possible duplication of flow files");
--- End diff --
Thinking through this error message and how it would be useful to a user, I
would like some kind of UUID to output here (like a message id) but there
aren't any in MQTT. So I think it would be better to word the warning a
different way by referencing the FlowFile that could potentially contain
duplicate data. By having a warning message with the UUID of the FlowFile
containing potentially duplicate data the user may be able to correlate that
using provenance to find the other FlowFile with duplicate data.
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