Github user ptgoetz commented on a diff in the pull request:
https://github.com/apache/storm/pull/991#discussion_r49160828
--- Diff:
external/storm-mqtt/core/src/main/java/org/apache/storm/mqtt/trident/MqttPublishFunction.java
---
@@ -0,0 +1,84 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.storm.mqtt.trident;
+
+import backtype.storm.Config;
+import backtype.storm.task.OutputCollector;
+import backtype.storm.topology.FailedException;
+import org.apache.storm.mqtt.MqttMessage;
+import org.apache.storm.mqtt.common.MqttOptions;
+import org.apache.storm.mqtt.MqttTupleMapper;
+import org.apache.storm.mqtt.common.MqttPublisher;
+import org.apache.storm.mqtt.common.SslUtils;
+import org.apache.storm.mqtt.ssl.KeyStoreLoader;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import storm.trident.operation.BaseFunction;
+import storm.trident.operation.TridentCollector;
+import storm.trident.operation.TridentOperationContext;
+import storm.trident.tuple.TridentTuple;
+
+import java.util.Map;
+
+public class MqttPublishFunction extends BaseFunction {
--- End diff --
I thought about that distinction. Ultimately, I decided upon a function
based on the following criteria:
1, There is no bulk publishing mechanism with MQTT, so there wouldn't be
any performance benefit in processing tuples in batch.
2. Aside from publishing a message with a QoS of 2, we don't have any way
to truly determine if it reached all subscribers, only the broker, and if the
broker dies...??
3. Exactly once is virtually impossible with MQTT in a distributed
environment.
4. Most MQTT use cases that need to scale avoid QoS 2 because of the
overhead.
That being said, I'm perfectly open to exploring a MQTT State
implementation if it would be useful.
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