KAFKA-4936: Add dynamic routing in Streams by guozhangwang · Pull Request #5018 · apache/kafka

guozhangwang · 2018-05-15T05:36:27Z

Add the proposed APIs as described in https://cwiki.apache.org/confluence/display/KAFKA/KIP-303%3A+Add+Dynamic+Routing+in+Streams+Sink.
Modify StreamPartitioner#partition to include topic name along with this change, since now it is less reasonable to ignore the topic name since it may not be pre-known.
Update TopologyDescription#Sink implementation: when the topic name is static, print the topic name, otherwise print the dynamic topic name extractor class name.

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…namic-routing-on-sink

…eExtractor.java

mjsax · 2018-05-17T23:19:27Z

\cc @bbejeck @vvcephei

mjsax

Thanks for the PR!

mjsax · 2018-05-17T23:20:27Z

+     * {@link StreamsConfig stream configuration}.
+     *
+     * @param name              the unique name of the sink
+     * @param topicExtractor    the mapper to dynamically choose the name of the Kafka topic to which this sink should write per reach record


typo: per reach record

mjsax · 2018-05-17T23:21:19Z

    }

+    /**
+     * Add a new sink that forwards records from upstream parent processor and/or source nodes to Kafka topics dynamically.


IMHO, "dynamically" need a little bit more explanation. Should we also state, that all those topics must be created by the user manually?

I agree with "dynamically"... maybe "based on the {@code topicExtractor}"?

About the second point, I think that's addressed in the following line.

+1 to "based on the {@code topicExtractor}"

mjsax · 2018-05-17T23:21:57Z

+     * @param name              the unique name of the sink
+     * @param topicExtractor    the mapper to dynamically choose the name of the Kafka topic to which this sink should write per reach record
+     * @param parentNames       the name of one or more source or processor nodes whose output records this sink should consume
+     *                          and write to its topic


its topic -> need rephrasing ?

mjsax · 2018-05-17T23:22:42Z

+     * @param parentNames       the name of one or more source or processor nodes whose output records this sink should consume
+     *                          and write to its topic
+     * @return                  itself
+     * @throws TopologyException if parent processor is not added yet, or if this processor's name is equal to the parent's name


we also throw if name is not unique?

mjsax · 2018-05-17T23:22:49Z

+     * @see #addSink(String, String, Serializer, Serializer, StreamPartitioner, String...)
+     */
+    public synchronized <K, V> Topology addSink(final String name,
+                                         final TopicNameExtractor<K, V> topicExtractor,


nit: fix indention

mjsax · 2018-05-17T23:42:13Z

+     * does not exist in the Kafka cluster.
+     *
+     * @param key           the record key
+     * @param value         the record value payload


remove payload ?

mjsax · 2018-05-17T23:42:44Z

+     * @param key           the record key
+     * @param value         the record value payload
+     * @param recordContext current context metadata of the record
+     * @return the topic name to send to


the topic name the record should be sent to ?

mjsax · 2018-05-17T23:48:18Z

            throw new StreamsException("Invalid (negative) timestamp of " + timestamp + " for output record <" + key + ":" + value + ">.");
        }

+        final String topic = topicExtractor != null ? topicExtractor.extract(key, value, this.context.recordContext()) : this.topic;


I am wondering, if we should always use a TopicNameExtractor. Ie, if a topic is given, we create a TopicNameExtractor that always return the topic name?

I tend to agree, would be consistent with other approaches like the StateRestoreListener

I tend to not do that because it would be one extra function call on each record to send to.

Not sure what is more performant: a function call (that might get inlined via JIT) or evaluating the branch-condition that would also be optimized during runtime quite a bit.... Was just a thought. Not sure if there will be a big difference between both during runtime.

I'll go ahead and make the change, with some optimizations on runtime window partitioner check.

mjsax · 2018-05-17T23:49:50Z

+        stream.to(new TopicNameExtractor<String, String>() {
+            @Override
+            public String extract(String key, String value, RecordContext recordContext) {
+                return recordContext.topic() + "-" + key + "-topic";


Why not just use the key itself?

I wanted to check that the record context fields and the key value are accessible in this test.

Should be two tests instead? (Leave it up to you to decide -- don't insist on a change)

mjsax · 2018-05-17T23:51:32Z

+    * // to the through call
+    * }}}
+    *
+    * @param extractor the mapper from key value to topic name


should be updated?

bbejeck

left a couple of comments

bbejeck · 2018-05-18T20:57:16Z

            throw new StreamsException("Invalid (negative) timestamp of " + timestamp + " for output record <" + key + ":" + value + ">.");
        }

+        final String topic = topicExtractor != null ? topicExtractor.extract(key, value, this.context.recordContext()) : this.topic;


I tend to agree, would be consistent with other approaches like the StateRestoreListener

bbejeck · 2018-05-18T21:10:05Z

-                // prefix the internal topic name with the application id
-                return new SinkNode<>(name, decorateTopic(topic), keySerializer, valSerializer, partitioner);
+            if (topic != null) {
+                if (internalTopicNames.contains(topic)) {


Maybe extract lines 361-363 to a method named something like createSinkNodeWithTopic returning a SinkNode then this method body would just have single if-else statement. But not a big deal could stay as is.

I think it is okay to keep as is since this function will only be called once so no harm to just inline it.

…namic-routing-on-sink

mjsax · 2018-05-19T21:14:10Z

     *
     * @param name              the unique name of the sink
-     * @param topicExtractor    the mapper to dynamically choose the name of the Kafka topic to which this sink should write per reach record
+     * @param topicExtractor    the extractor to determine the name of the Kafka topic to which this sink should write for reach record


typo reach should be each (Might be somewhere else, too. Please double check.)

mjsax · 2018-05-19T21:15:10Z

+     *                          and dynamically write to topics
     * @return                  itself
-     * @throws TopologyException if parent processor is not added yet, or if this processor's name is equal to the parent's name
+     * @throws TopologyException if parent processor is not added yet, or if this processor's name is not unique


I think we throw for all three cases.

this processor's name is equal to the parent's name is subsumed by this processor's name is not unique, right?

I don't think so. If A connects to itself, it's still a single node:

topology.addSource("source",...); topology.addProcessor("name", ..., "parent"); // throws because "parent" no added yet topology.addProcessor("source", ...); // throws because "source" is already used topology.addProcessor("processor", ..., "processor"); // throws because it connects to itself --- note that internally, we would add "processor" first before setting up the connection (ie, the parent is know then setting up the connection as we just added the parent) --- however, we do have an additional check in the code to throw if people build a loop like this

Make sense, will add it back.

mjsax · 2018-05-19T21:17:15Z

    * }}}
    *
-    * @param extractor the mapper from key value to topic name
+    * @param extractor the extractor to determine the name of the Kafka topic to write to for reach record


reach -> each

guozhangwang · 2018-05-20T01:42:24Z

@mjsax my current solution is to test

if (partitioner instanceof WindowedStreamPartitioner && ((WindowedStreamPartitioner) partitioner).topic() == null) {
                    partition = ((WindowedStreamPartitioner) partitioner).partition(topic, (Windowed) key, value, partitions.size());

at runtime, which should work but a bit ugly. I think it is OK for this PR itself.

mjsax · 2018-05-20T04:31:26Z

Agreed -- didn't want to imply to fix it with this PR. But might be worth to fix properly with a follow up KIP.

guozhangwang · 2018-05-20T04:55:45Z

Agreed -- didn't want to imply to fix it with this PR. But might be worth to fix properly with a follow up KIP.

Sounds good, I'll create a JIRA.

…namic-routing-on-sink

bbejeck

Thanks, @guozhangwang, just one minor comment otherwise LGTM.

bbejeck · 2018-05-21T15:25:03Z

+public interface TopicNameExtractor<K, V> {
+
+    /**
+     * Extracts the topic name to send to. The topic name must be pre-existed, since the Kafka Streams library will not


nit: The topic name must be pre-existed -> The returned topic name must already exist

…namic-routing-on-sink

guozhangwang · 2018-05-21T18:02:40Z

@mjsax while working on the window stream partitioner along with merging single topic to topic extractor, I realized the root cause is because in StreamPartitioner interface we do not pass in the topic name, which makes less sense while we are adding dynamic routing to sink node since the topic name would not be able to always pre-known.

So I'm modifying this and include it as part of the public API changes in the KIP wiki. Will ask for recasting the vote.

The previous ugly solution I had has a performance issue, as it checks instanceof and try to do the casting on each record call; note that during the build phase as we 1) decorate the internal topic name, 2) generate sink nodes, generate sink descriptions 3) etc, it is a one-time thing so we do not need to worry.

mjsax · 2018-05-21T18:15:36Z

@guozhangwang Sounds good to me!

guozhangwang · 2018-05-21T18:44:43Z

@mjsax @bbejeck updated PR for reviews again. Also updated the description for the core changes.

…namic-routing-on-sink

mjsax · 2018-05-21T19:57:29Z

+            if (topicNameExtractor instanceof StaticTopicNameExtractor)
+                return ((StaticTopicNameExtractor) topicNameExtractor).topicName;
+            else
+                return topicNameExtractor.getClass().getName();


Why do we return the class name here? Maybe return null indicating unknown?

Since this is for string typed printing, I felt printing the class name is more informative than returning a null. WDYT?

If this method is used only for informational purposes, maybe we should just call toString on the topicNameExtractor and make sure that the StaticTopicNameExtractor includes the topic name in its output. Better yet, we could just change the method to return the topicNameExtractor itself, since it really doesn't have a topic anymore.

If it's used for any other not-strictly-informational purpose, it seems risky to return some other string, claiming it's the "topic". It seems like it could become a bug in the future...

mjsax · 2018-05-21T19:58:36Z

+        this.topicName = topicName;
+    }
+
+    public String extract(K key, V value, RecordContext recordContext) {


nit: add final

guozhangwang · 2018-05-22T00:41:51Z

@mjsax updated on comments again.

mjsax · 2018-05-22T01:24:54Z

One last thing: we need to update the docs accordingly.

guozhangwang · 2018-05-22T01:29:22Z

One last thing: we need to update the docs accordingly.

Yup, that's my plan once the KIP is accepted, and the public changes are final.

bbejeck · 2018-05-22T14:46:22Z

retest this please

bbejeck

Updates LGTM

…namic-routing-on-sink

guozhangwang · 2018-05-22T18:27:09Z

@mjsax @bbejeck @vvcephei added docs for KIP-303.

…namic-routing-on-sink

add record context

guozhangwang · 2018-05-23T00:41:09Z

@@ -1,81 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one or more


This is removed as its functionality is completely replaced with ProcessorRecordContext now.

mjsax · 2018-05-23T01:13:01Z

        Forwarding based on child index is not supported in the new API any longer.
    </p>
+    <p>
+        We have added support to allow dynamically routing records to Kafka topics. More specifically, in both the lower-level <code>Topology#addSink</code> and higher-level <code>KStream#to</code> APIs, we have added variants that


We have added support to allow routing records dynamically to Kafka topics. ?

mjsax · 2018-05-23T01:13:28Z

    </p>
+    <p>
+        We have added support to allow dynamically routing records to Kafka topics. More specifically, in both the lower-level <code>Topology#addSink</code> and higher-level <code>KStream#to</code> APIs, we have added variants that
+        takes a <code>TopicNameExtractor</code> instance instead of a specific <code>String</code> topic name, such that for each received record from the upstream processor, the library will dynamically determine which Kafka topic to write to


specific topic name (i.e., a <code>String</code>) ?

mjsax · 2018-05-23T01:14:46Z

+    <p>
+        We have added support to allow dynamically routing records to Kafka topics. More specifically, in both the lower-level <code>Topology#addSink</code> and higher-level <code>KStream#to</code> APIs, we have added variants that
+        takes a <code>TopicNameExtractor</code> instance instead of a specific <code>String</code> topic name, such that for each received record from the upstream processor, the library will dynamically determine which Kafka topic to write to
+        based on the record's key and value, as well as record context. Note that all the Kafka topics that may possibly to write to are still considered as user topics and hence required to be pre-created. In addition to that, we have modified the


that may possibly be used are

mjsax · 2018-05-23T01:17:26Z

    }

+    @Override
+    public boolean equals(final Object o) {


Why do we need equals() and hashCode() now?

To make bugWarnings happy

Why was bugWarnings unhappy? Is this class used in an equals comparison somewhere? Or maybe a collection?

I think bugwarning requires any objects that is used as key in a map to override these two functions.

…namic-routing-on-sink

vvcephei · 2018-05-24T15:23:57Z

+    protected final long offset;
+    protected final String topic;
+    protected final int partition;
+    protected final Headers headers;


Am I right in thinking that these are only exposed so that LRUCacheEntry can use them in equals/hashcode? If so, can it instead invoke the getters and keep these private?

vvcephei · 2018-05-24T18:21:56Z

    </p>
+    <p>
+        We have added support to allow routing records dynamically to Kafka topics. More specifically, in both the lower-level <code>Topology#addSink</code> and higher-level <code>KStream#to</code> APIs, we have added variants that
+        takes a <code>TopicNameExtractor</code> instance instead of a specific <code>String</code> typed topic name, such that for each received record from the upstream processor, the library will dynamically determine which Kafka topic to write to


takes -> take

vvcephei · 2018-05-24T18:27:43Z

    }

+    /**
+     * Add a new sink that forwards records from upstream parent processor and/or source nodes to Kafka topics dynamically.


I agree with "dynamically"... maybe "based on the {@code topicExtractor}"?

About the second point, I think that's addressed in the following line.

vvcephei · 2018-05-24T18:28:53Z

+    }
+
+    /**
+     * Add a new sink that forwards records from upstream parent processor and/or source nodes to Kafka topics dynamically,


vvcephei · 2018-05-24T18:29:07Z

+    }
+
+    /**
+     * Add a new sink that forwards records from upstream parent processor and/or source nodes to Kafka topics dynamically.


vvcephei · 2018-05-24T18:30:45Z

+    void to(final TopicNameExtractor<K, V> topicExtractor);
+
+    /**
+     * Dynamically materialize this stream to topics using default serializers specified in the config.


This one doesn't use the default serializers, but instead uses produced, right?

vvcephei · 2018-05-24T18:42:22Z

+            if (topicNameExtractor instanceof StaticTopicNameExtractor)
+                return ((StaticTopicNameExtractor) topicNameExtractor).topicName;
+            else
+                return topicNameExtractor.getClass().getName();


If this method is used only for informational purposes, maybe we should just call toString on the topicNameExtractor and make sure that the StaticTopicNameExtractor includes the topic name in its output. Better yet, we could just change the method to return the topicNameExtractor itself, since it really doesn't have a topic anymore.

If it's used for any other not-strictly-informational purpose, it seems risky to return some other string, claiming it's the "topic". It seems like it could become a bug in the future...

vvcephei · 2018-05-24T19:07:11Z

+        stream.to(new TopicNameExtractor<String, String>() {
+            @Override
+            public String extract(String key, String value, RecordContext recordContext) {
+                return recordContext.topic() + "-" + key + "-" + value.substring(0, 1);


we're in Java8 now... I think you can do: (key,value,context) -> { ... }

Will that make this code easier or harder to read... who can say?

vvcephei · 2018-05-24T19:09:32Z

        hostToPartitions.put(hostThree, Collections.singleton(topic3P0));

-        partitionInfos = Arrays.asList(
+        List<PartitionInfo> partitionInfos = Arrays.asList(


bbejeck

Just added one minor comment, otherwise LGTM with latest changes.

bbejeck · 2018-05-24T19:28:11Z

    }

+    /**
+     * Add a new sink that forwards records from upstream parent processor and/or source nodes to Kafka topics dynamically.


+1 to "based on the {@code topicExtractor}"

…namic-routing-on-sink

guozhangwang · 2018-05-30T01:28:14Z

I've addressed the meta comment on SinkNode#topicName to make its retruned value nullable.

mjsax

LGTM.

Waiting for either @bbejeck or @vvcephei to approve before merging.

implements KIP-303 Reviewers: Bill Bejeck <bill@confluent.io>, John Roesler <john@confluent.io>, Matthias J. Sax <matthias@confluent.io>

guozhangwang added 4 commits May 14, 2018 22:35

add dyanmic routing

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add new interface than reusing existing one

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add streams/src/main/java/org/apache/kafka/streams/processor/TopicNam…

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…eExtractor.java

guozhangwang changed the title ~~KAFKA-4936: Add dynamic routing in Streams [DO NOT MERGE]~~ KAFKA-4936: Add dynamic routing in Streams May 17, 2018

update scala api

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docs for KIP-303

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expose record context as public API

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guozhangwang deleted the K4936-dynamic-routing-on-sink branch April 24, 2020 23:57

mjsax added the kip Requires or implements a KIP label Jun 13, 2020

		@@ -1,81 +0,0 @@
		/*
		* Licensed to the Apache Software Foundation (ASF) under one or more

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