Streams Upgrade Guide

Contents

Upgrading from Confluent Platform 4.1.x (Kafka 1.1.x-cp1) to Confluent Platform 5.0.0 (Kafka 2.0.0-cp1)

Compatibility

Kafka Streams applications built with Confluent Platform 5.0.0 (Kafka 2.0.0-cp1) are forward and backward compatible with certain Kafka clusters.

  • Forward-compatible to Confluent Platform 5.0.0 clusters (Kafka 2.0.0-cp1): Existing Kafka Streams applications built with Confluent Platform 3.0.x (Kafka 0.10.0.x-cp1), Confluent Platform 3.1.x (Kafka 0.10.1.x-cp2), Confluent Platform 3.2.x (Kafka 0.10.2.x-cp1), Confluent Platform 3.3.x (Kafka 0.11.0.x-cp1), Confluent Platform 4.0.x (Kafka 1.0.x-cp1) or Confluent Platform 4.1.x (Kafka 1.1.x-cp1) will work with upgraded Kafka clusters running Confluent Platform 5.0.0 (Kafka 2.0.0-cp1).
  • Backward-compatible to older clusters down to Confluent Platform 3.1.x (Kafka 0.10.1.x-cp2): New Kafka Streams applications built with Confluent Platform 5.0.0 (Kafka 2.0.0-cp1) will work with older Kafka clusters running Confluent Platform 3.1.x (Kafka 0.10.1.x-cp2), Confluent Platform 3.2.x (Kafka 0.10.2.x-cp1), Confluent Platform 3.3.x (Kafka 0.11.0.x-cp1), Confluent Platform 4.0.x (Kafka 1.0.x-cp1) or Confluent Platform 4.1.x (Kafka 1.1.x-cp1). However, when exactly-once processing guarantee is required, your Kafka cluster needs to be upgraded to at least Confluent Platform 3.3.x (Kafka 0.11.0.x-cp1). Note, that exactly-once feature is disabled by default and thus a rolling bounce upgrade of your Streams application is possible if you don’t enable this new feature explicitly. Kafka clusters running Confluent Platform 3.0.x (Kafka 0.10.0.x-cp1) are not compatible with new Confluent Platform 5.0.0 Kafka Streams applications.

Note

As of Confluent Platform 4.0.0 (Kafka 1.0.0-cp1), Kafka Streams requires message format 0.10 or higher. Thus, if you kept an older message format when upgrading your brokers to Confluent Platform 3.1 (Kafka 0.10.1-cp1) or a later version, Kafka Streams Confluent Platform 5.0.0 (Kafka 2.0.0-cp1) won’t work. You will need to upgrade the message format to 0.10 before you upgrade your Kafka Streams application to Confluent Platform 5.0.0 (Kafka 2.0.0-cp1) or newer.

Compatibility Matrix:

 
Kafka Broker (columns)
Streams API (rows)
3.0.x / 0.10.0.x
3.1.x / 0.10.1.x and
3.2.x / 0.10.2.x
3.3.x / 0.11.0.x and
4.0.x / 1.0.x and
4.1.x / 1.1.x and
5.0.x / 2.0.x
3.0.x / 0.10.0.x
compatible
compatible
compatible
3.1.x / 0.10.1.x and
3.2.x / 0.10.2.x
 
compatible
compatible
3.3.x / 0.11.0.x
 
compatible with exactly-once turned
off (requires broker version
Confluent Platform 3.3.x or higher)
compatible
4.0.x / 1.0.x and
4.1.x / 1.1.x and
5.0.x / 2.0.x
 
compatible with exactly-once turned
off (requires broker version
Confluent Platform 3.3.x or higher);
requires message format 0.10 or higher
compatible;
requires message format
0.10 or higher

The Streams API is not compatible with Kafka clusters running older Kafka versions (0.7, 0.8, 0.9).

Upgrading your Kafka Streams applications to Confluent Platform 5.0.0

To make use of Confluent Platform 5.0.0 (Kafka 2.0.0-cp1), you need to update the Kafka Streams dependency of your application to use the version number 2.0.0-cp1, and you may need to make minor code changes (details below), and then recompile your application.

For example, in your pom.xml file:

<dependency>
    <groupId>org.apache.kafka</groupId>
    <artifactId>kafka-streams</artifactId>
    <!-- update version to 2.0.0-cp1 -->
    <version>2.0.0-cp1</version>
</dependency>

There are some Streams API changes in Confluent Platform 5.0.0, if your application uses them, then you need to update your code accordingly.

Note

As of Confluent Platform 4.0.0 (Kafka 1.0.0-cp1) a topology regression was introduced when source KTable instances were changed to have changelog topics instead of re-using the source topic. As of Confluent Platform 5.0.0 (Kafka 2.0.0-cp1) KTable instances re-using the source topic as the changelog topic has been reinstated, but is optional and must be configured by setting StreamsConfig.TOPOLOGY_OPTIMIZATION to StreamsConfig.OPTIMIZE.

This brings up some different scenarios depending on what you are upgrading from and what you are upgrading to.

  • If you are upgrading from using KStreamBuilder version Kafka 1.0.x-cp1/1.1.x-cp1 to StreamsBuilder Kafka 2.0.0-cp1 it’s recommended to enable the optimization as there are no changes to your topology. Please note that if you elect not to enable the optimization, there is a small window of time for possible data loss until the changelog topic contains one record per key.
  • If you are upgrading from using StreamsBuilder version Kafka 1.0.x-cp1/1.1.x-cp1 to Kafka 2.0.0-cp-1 you can enable the optimization, but your topology will change so you’ll need to restart your application with a new application ID. Additionally, if you want to perform a rolling upgrade, it is recommended not to enable the optimization. If you elect not to enable the optimization, then no further changes are required.

Additionally, when starting with a new application ID, you can possibly end up reprocessing data, since the application ID has been changed. If you don’t want to reprocess records, you’ll need to create new output topics, so downstream user can cut over in a controlled fashion.

API changes

New Streams configurations and public interfaces are added, and deprecated APIs are removed.

Skipped Records Metrics Refactored

Starting with Confluent Platform 5.0.0, Kafka Streams does not report the skippedDueToDeserializationError-rate and skippedDueToDeserializationError-total metrics.

Deserialization errors, and all other causes of record skipping, are now accounted for in the pre-existing metrics skipped-records-rate and skipped-records-total. When a record is skipped, the event is now logged at WARN level. Note these metrics are mainly for monitoring unexpected events; If there are systematic issues that caused too many unprocessable records to be skipped, and hence the resulted warning logs become burdensome, you should consider filtering our these unprocessable records instead of depending on record skipping semantics. For more details, see KIP-274.

As of right now, the potential causes of skipped records are:

  • null keys in table sources.
  • null keys in table-table inner/left/outer/right joins.
  • null keys or values in stream-table joins.
  • null keys or values in stream-stream joins.
  • null keys or values in aggregations / reductions / counts on grouped streams.
  • null keys in aggregations / reductions / counts on windowed streams.
  • null keys in aggregations / reductions / counts on session-windowed streams.
  • Errors producing results, when the configured default.production.exception.handler decides to CONTINUE (the default is to FAIL and throw an exception).
  • Errors deserializing records, when the configured default.deserialization.exception.handler decides to CONTINUE (the default is to FAIL and throw an exception). This was the case previously captured in the skippedDueToDeserializationError metrics.
  • Fetched records having a negative timestamp.

New Functions in Window Store Interface

Confluent Platform now supports methods in ReadOnlyWindowStore which allows you to query the key-value pair of a single window. If you have customized window store implementations on the above interface, you must update your code to implement the newly added method. For more details, see KIP-261.

Simplified KafkaStreams Constructor

The KafakStreams constructor was simplfied. Instead of requiring the user to create a boilderplate StreamsConfig object, the constructor now directly accepts the Properties object that specifies the actual user configuration.

StreamsBuilder builder = new StreamsBuilder();
// define processing logic
Topology topology = builder.build();

// or

Topology topology = new Topology();
// define processing logic


Properties props = new Properties();
// define configuration


// old API

KafkaStream stream = new KafkaStreams(topology, new StreamsConfig(props));
KafkaStream stream = new KafkaStreams(topology, new StreamsConfig(props), /* pass in KafkaClientSupplier or Time */);


// new API

KafkaStream stream = new KafkaStreams(topology, props);
KafkaStream stream = new KafkaStreams(topology, props, /* pass in KafkaClientSupplier or Time */);

Support Dynamic Routing at Sink

In this release you can now dynamically route records to Kafka topics. More specifically, in both the lower-level Topology#addSink and higher-level KStream#to APIs, we have added variants that take a TopicNameExtractor instance instead of a specific String topic name. For each record received from the upstream processor, the TopicNameExtractor 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 output Kafka topics are still considered user topics and hence must be pre-created. Also, we have modified the StreamPartitioner interface to add the topic name parameter since the topic name now may not be known beforehand; users who have customized implementations of this interface would need to update their code while upgrading their application.

Support Message Headers

In this release there is message header support in the Processor API. In particular, we have added a new API ProcessorContext#headers() which returns a Headers object that keeps track of the headers of the source topic’s message that is being processed. Through this object, users can manipulate the headers map that is being propagated throughout the processor topology as well, for example Headers#add(String key, byte[] value) and Headers#remove(String key). When Streams DSL is used, users can call process or transform in which they can also access the ProcessorContext to access and manipulate the message header; if user does not manipulate the header, it will still be preserved and forwarded while the record traverses through the processor topology. When the resulted record is sent to the sink topics, the preserved message header will also be encoded in the sent record.

KTable Now Supports Transform Values

In this release another new API, KTable#transformValues, was added. For more information, see KIP-292 <https://cwiki.apache.org/confluence/display/KAFKA/KIP-292%3A+Add+transformValues%28%29+method+to+KTable> __.

Improved Windowed Serde Support

We added helper class WindowedSerdes that allows you to create time- and session-windowed serdes without the need to know the details how windows are de/serialized. The created window serdes wrap a user-provided serde for the inner key- or value-data type. Furthermore, two new configs default.windowed.key.serde.inner and default.windowed.value.serde.inner were added that allow to specify the default inner key- and value-serde for windowed types. Note, these new configs are only effective, if default.key.serde or default.value.serde specifies a windowed serde (either WindowedSerdes.TimeWindowedSerde or WindowedSerdes.SessionWindowedSerde).

Allow Timestamp Manipulation

Using the Processor API, it is now possible to set the timestamp for output messages explicitly. This change implies updates to the ProcessorContext#forward() method. Some existing methods were deprecated and replaced by new ones. In particular, it is not longer possible to send records to a downstream processor based on its index.

// old API

public class MyProcessor implements Processor<String, Integer> {
  private ProcessorContext context;

  @Override
  public void init(ProcessorContext context) {
    this.context = context;
  }

  @Override
  public void process(String key, Integer value) {
    // do some computation

    // send record to all downstream processors
    context.forward(newKey, newValue);
    // send record to particular downstream processors (if it exists; otherwise drop record)
    context.forward(newKey, newValue, "downstreamProcessorName");
    // send record to particular downstream processors per index (throws if index is invalid)
    int downStreamProcessorIndex = 2;
    context.forward(newKey, newValue, downstreamProcessorIndex);
  }

  @Override
  public void close() {} // nothing to do
}


// new API

public class MyProcessor implements Processor<String, Integer> {
  // omit other methods that don't change for brevity

  @Override
  public void process(String key, Integer value) {
    // do some computation

    // send record to all downstream processors
    context.forward(newKey, newValue); // same as old API
    context.forward(newKey, newValue, To.all()); // new; same as line above
    // send record to particular downstream processors (if it exists; otherwise drop record)
    context.forward(newKey, newValue, To.child("downstreamProcessorName"));
    // send record to particular downstream processors per index (throws if index is invalid)
    // -> not supported in new API

    // new: set record timestamp
    long outputRecordTimestamp = 42L;
    context.forward(newKey, newValue, To.all().withTimestamp(outputRecordTimestamp));
    context.forward(newKey, newValue, To.child("downstreamProcessorName").withTimestamp(outputRecordTimestamp));
  }
}

Public Test-Utils Artifact

Confluent Platform now ships with a kafka-streams-test-uitls artifact that contains utility classes to unit test your Kafka Streams application. Check out Testing Streams Code section for more details.

Scala API

Confluent Platform now ships with the Apache Kafka Scala API for Kafka Streams. You can add the dependency for Scala 2.11 or 2.12 artifacts:

<dependency>
    <groupId>org.apache.kafka</groupId>
    <artifactId>kafka-streams-scala_2.11</artifactId>
    <!-- or Scala 2.12
    <artifactId>kafka-streams-scala_2.12</artifactId>
    -->
    <version>2.0.0-cp1</version>
</dependency>

Deprecated APIs are Removed

The following deprecated APIs are removed in Confluent Platform 5.0.0:

  1. KafkaStreams#toString no longer returns the topology and runtime metadata; to get topology metadata you can call Topology#describe(), and to get thread runtime metadata you can call KafkaStreams#localThreadsMetadata (deprecated since Confluent Platform 4.0.0). For detailed guidance on how to update your code please read here.
  2. TopologyBuilder and KStreamBuilder are removed and replaced by Topology and StreamsBuidler respectively (deprecated since Confluent Platform 4.0.0).
  3. StateStoreSupplier are removed and replaced with StoreBuilder (deprecated since Confluent Platform 4.0.0); and the corresponding Stores#create and KStream, KTable, KGroupedStream‘s overloaded functions that use it have also been removed.
  4. KStream, KTable, KGroupedStream overloaded functions that requires serde and other specifications explicitly are removed and replaced with simpler overloaded functions that use Consumed, Produced, Serialized, Materialized, Joined (deprecated since Confluent Platform 4.0.0).
  5. Processor#punctuate, ValueTransformer#punctuate, ValueTransformer#punctuate and RecordContext#schedule(long) are removed and replaced by RecordContext#schedule(long, PunctuationType, Punctuator) (deprecated since Confluent Platform 4.0.0).
  6. The second boolean typed parameter loggingEnabled in ProcessorContext#register has been removed; you can now use StoreBuilder#withLoggingEnabled, #withLoggingDisabled to specify the behavior when they create the state store (deprecated since Confluent Platform 3.3.0).
  7. KTable#writeAs, #print, #foreach, #to, #through are removed as their semantics are more confusing than useful, you can call KTable#tostream()#writeAs etc instead for the same purpose (deprecated since Confluent Platform 3.3.0).
  8. StreamsConfig#KEY_SERDE_CLASS_CONFIG, #VALUE_SERDE_CLASS_CONFIG, #TIMESTAMP_EXTRACTOR_CLASS_CONFIG are removed and replaced with StreamsConfig#DEFAULT_KEY_SERDE_CLASS_CONFIG, #DEFAULT_VALUE_SERDE_CLASS_CONFIG, #DEFAULT_TIMESTAMP_EXTRACTOR_CLASS_CONFIG respectively (deprecated since Confluent Platform 3.3.0).
  9. StreamsConfig#ZOOKEEPER_CONNECT_CONFIG is removed as we do not need ZooKeeper dependency in Streams any more (deprecated since Confluent Platform 3.2.0).

Full upgrade workflow

A typical workflow for upgrading Kafka Streams applications from Confluent Platform 4.1.x to Confluent Platform 5.0.0 has the following steps:

  1. Upgrade your application: See upgrade instructions above.
  2. Stop the old application: Stop the old version of your application, i.e. stop all the application instances that are still running the old version of the application.
  3. Optional, upgrade your Kafka cluster: See kafka upgrade instructions. Note, if you want to use exactly-once processing semantics, upgrading your cluster to at least Confluent Platform 3.3.x is mandatory.
  4. Start the upgraded application: Start the upgraded version of your application, with as many instances as needed. By default, the upgraded application will resume processing its input data from the point when the old version was stopped (see previous step).

Upgrading older Kafka Streams applications to Confluent Platform 5.0.0

API changes (from Confluent Platform 4.0 to Confluent Platform 4.1)

A few new Streams configurations and public interfaces are added into Confluent Platform 4.1.x release.

Changes in bin/kafka-streams-application-reset

Added options to specify input topics offsets to reset according to KIP-171.

Embedded Admin Client Configuration

You can now customize the embedded admin client inside your Streams application which would be used to send all the administrative requests to Kafka brokers, such as internal topic creation, etc. This is done via the additional KafkaClientSupplier#getAdminClient(Map<String, Object>) interface; for example, users can provide their own AdminClient implementations to override the default ones in their integration testing. In addition, users can also override the configs that are passed into KafkaClientSupplier#getAdminClient(Map<String, Object>) to configure the returned AdminClient. Such overridden configs can be specified via the StreamsConfig by adding the admin configs with the prefix as defined by StreamsConfig#adminClientPrefix(String). Any configs that aren’t admin client configs will be ignored.

For example:

Properties streamProps = ...;
// use retries=10 for the embedded admin client
streamsProps.put(StreamsConfig.adminClientPrefix("retries"), 10);

API changes (from Confluent Platform 3.3 to Confluent Platform 4.0)

Kafka Streams and its API were improved and modified in the Confluent Platform 4.0.x release. All of these changes are backward compatible, thus it’s not require to update the code of your Kafka Streams applications immediately. However, some methods were deprecated and thus it is recommend to update your code eventually to allow for future upgrades. In this section we focus on deprecated APIs.

Building and running a topology

The two main classes to specify a topology, KStreamBuilder and TopologyBuilder, were deprecated and replaced by StreamsBuilder and Topology. Note, that both new classes are in package org.apache.kafka.streams and that StreamsBuilder does not extend Topology, i.e., the class hierarchy is different now. This change also affects KafkaStreams constructors that now only accept a Topology. If you use StreamsBuilder you can obtain the constructed topology via StreamsBuilder#build().

The new classes have basically the same methods as the old ones to build a topology via DSL or Processor API. However, some internal methods that were public in KStreamBuilder and TopologyBuilder, but not part of the actual API, are no longer included in the new classes.

// old API

KStreamBuilder builder = new KStreamBuilder(); // for DSL
// or
TopologyBuilder builder = new TopologyBuilder(); // for Processor API

Properties props = new Properties();
KafkaStreams streams = new KafkaStreams(builder, props);

// new API

StreamsBuilder builder = new StreamsBuilder(); // for DSL
// ... specify computational logic
Topology topology = builder.build();
// or
Topology topology = new Topology(); // for Processor API

Properties props = new Properties();
KafkaStreams streams = new KafkaStreams(topology, props);

Describing topology and stream task metadata

KafkaStreams#toString() and KafkaStreams#toString(final String indent), which were previously used to retrieve the user-specified processor topology information as well as runtime stream tasks metadata, are deprecated in 4.0.0. Instead, a new method of KafkaStreams, namely localThreadsMetadata() is added which returns an org.apache.kafka.streams.processor.ThreadMetadata object for each of the local stream threads that describes the runtime state of the thread as well as its current assigned tasks metadata. Such information will be very helpful in terms of debugging and monitoring your streams applications. For retrieving the specified processor topology information, users can now call Topology#describe() which returns an org.apache.kafka.streams.TopologyDescription object that contains the detailed description of the topology (for DSL users they would need to call StreamsBuilder#build() to get the Topology object first).

Merging KStreams:

As mentioned above, KStreamBuilder was deprecated in favor of StreamsBuilder. Additionally, KStreamBuilder#merge(KStream...) was replaced by KStream#merge(KStream) and thus StreamsBuilder does not have a merge() method. Note: instead of merging an arbitrary number of KStream instances into a single KStream as in the old API, the new #merge() method only accepts a single KStream and thus merges two KStream instances into one. If you want to merge more than two KStream instances, you can call KStream#merge() multiple times.

// old API

KStreamBuilder builder = new KStreamBuilder();

KStream<Long, String> firstStream = ...;
KStream<Long, String> secondStream = ...;
KStream<Long, String> thirdStream = ...;

KStream<Long, String> mergedStream = builder.merge(
  firstStream,
  secondStream,
  thirdStream);

// new API

StreamsBuilder builder = new StreamsBuilder();

KStream<Long, String> firstStream = ...;
KStream<Long, String> secondStream = ...;
KStream<Long, String> thirdStream = ...;

KStream<Long, String> mergedStream = firstStream.merge(secondStream)
                                                .merge(thirdStream);

Punctuation functions

The Processor API was extended to allow users to schedule punctuate functions either based on event-time (i.e. PunctuationType.STREAM_TIME) or wall-clock-time (i.e. PunctuationType.WALL_CLOCK_TIME). Before this, users could only schedule based on event-time and hence the punctuate function was data-driven only. As a result, the original ProcessorContext#schedule is deprecated with a new overloaded function. In addition, the punctuate function inside Processor is also deprecated, and is replaced by the newly added Punctuator#punctuate interface.

// old API (punctuate defined in Processor, and schedule only with stream-time)

public class WordCountProcessor implements Processor<String, String> {

    private ProcessorContext context;
    private KeyValueStore<String, Long> kvStore;

    @Override
    @SuppressWarnings("unchecked")
    public void init(ProcessorContext context) {
        // keep the processor context locally because we need it in punctuate() and commit()
        this.context = context;

        // call this processor's punctuate() method every 1000 milliseconds
        this.context.schedule(1000);

        // retrieve the key-value store named "Counts"
        kvStore = (KeyValueStore) context.getStateStore("Counts");
    }

    @Override
    public void punctuate(long timestamp) {
        KeyValueIterator<String, Long> iter = this.kvStore.all();
        while (iter.hasNext()) {
            KeyValue<String, Long> entry = iter.next();
            context.forward(entry.key, entry.value.toString());
        }
        iter.close();

        // commit the current processing progress
        context.commit();
    }

    // .. other functions
}


// new API (punctuate defined in Punctuator, and schedule can be either stream-time or wall-clock-time)

public class WordCountProcessor implements Processor<String, String> {

    private ProcessorContext context;
    private KeyValueStore<String, Long> kvStore;

    @Override
    @SuppressWarnings("unchecked")
    public void init(ProcessorContext context) {
        // keep the processor context locally because we need it in punctuate() and commit()
        this.context = context;

        // retrieve the key-value store named "Counts"
        kvStore = (KeyValueStore) context.getStateStore("Counts");

        // schedule a punctuate() method every 1000 milliseconds based on stream time
        this.context.schedule(1000, PunctuationType.STREAM_TIME, (timestamp) -> {
            KeyValueIterator<String, Long> iter = this.kvStore.all();
            while (iter.hasNext()) {
                KeyValue<String, Long> entry = iter.next();
                context.forward(entry.key, entry.value.toString());
            }
            iter.close();

            // commit the current processing progress
            context.commit();
        });
    }

    // .. other functions
}

Streams Configuration

You can now override the configs that are used to create internal repartition and changelog topics. You provide these configs via the StreamsConfig by adding the topic configs with the prefix as defined by StreamsConfig#topicPrefix(String). Any properties in the StreamsConfig with the prefix will be applied when creating internal topics. Any configs that aren’t topic configs will be ignored. If you are already using StateStoreSupplier or Materialized to provide configs for changelogs, then they will take precedence over those supplied in the config.

For example:

Properties streamProps = ...;
// use cleanup.policy=delete for internal topics
streamsProps.put(StreamsConfig.topicPrefix("cleanup.policy"), "delete");

New classes for optional DSL parameters

Several new classes were introduced, i.e., Serialized, Consumed, Produced etc. to enable us to reduce the overloads in the DSL. These classes mostly have a static method with to create an instance, i.e., Serialized.with(Serdes.Long(), Serdes.String()).

Scala users should be aware that they will need to surround with with backticks.

For example:

// When using Scala: enclose "with" with backticks
Serialized.`with`(Serdes.Long(), Serdes.String())

API changes (from Confluent Platform 3.2 to Confluent Platform 3.3)

Kafka Streams and its API were improved and modified since the release of Confluent Platform 3.2.x. All of these changes are backward compatible, thus it’s not require to update the code of your Kafka Streams applications immediately. However, some methods and configuration parameters were deprecated and thus it is recommend to update your code eventually to allow for future upgrades. In this section we focus on deprecated APIs.

Streams Configuration

The following configuration parameters were renamed and their old names were deprecated.

  • key.serde renamed to default.key.serde
  • value.serde renamed to default.value.serde
  • timestamp.extractor renamed to default.timestamp.extractor

Thus, StreamsConfig#KEY_SERDE_CONFIG, StreamsConfig#VALUE_SERDE_CONFIG, and StreamsConfig#TIMESTAMP_EXTRACTOR_CONFIG were deprecated, too.

Additionally, the following method changes apply:

  • method keySerde() was deprecated and replaced by defaultKeySerde()
  • method valueSerde() was deprecated and replaced by defaultValueSerde()
  • new method defaultTimestampExtractor() was added

Local timestamp extractors

The Streams API was extended to allow users to specify a per stream/table timestamp extractor. This simplifies the usage of different timestamp extractor logic for different streams/tables. Before, users needed to apply an if-then-else pattern within the default timestamp extractor to apply different logic to different input topics. The old behavior introduced unnecessary dependencies and thus limited code modularity and code reuse.

To enable the new feature, the methods KStreamBuilder#stream(), KStreamBuilder#table(), KStream#globalTable(), TopologyBuilder#addSource(), and TopologyBuilder#addGlobalStore() have new overloads that allow to specify a “local” timestamp extractor that is solely applied to the corresponding input topics.

// old API (single default TimestampExtractor that is applied globally)

public class MyTimestampExtractor implements TimestampExtractor {
    @Override
    public long extract(ConsumerRecord record, long previousTimestamp) {
        long timestamp;

        String topic = record.topic();
        switch (topic) {
            case "streamInputTopic":
                timestamp = record.value().getDataTimestamp(); // assuming that value type has a method #getDataTimestamp()
                break;
            default:
                timestamp = record.timestamp();
        }

        if (timestamp < 0) {
            throw new RuntimeException("Invalid negative timestamp.");
        }

        return timestamp;
    }
}

KStreamBuilder builder = new KStreamBuilder();
KStream stream = builder.stream(keySerde, valueSerde, "streamInputTopic");
KTable table= builder.table("tableInputTopic");

Properties props = new Properties(); // omitting mandatory configs for brevity
// set MyTimestampExtractor as global default extractor for all topics
config.set("default.timestamp.extractor", MyTimestampExtractor.class);

KafkaStreams streams = new KafkaStreams(builder, props);


// new API (custom TimestampExtractor for topic "streamInputTopic" only; returns value embedded timestamp)

public class StreamTimestampExtractor implements TimestampExtractor {
    @Override
    public long extract(ConsumerRecord record, long previousTimestamp) {
        long timestamp = record.value().getDataTimestamp(); // assuming that value type has a method #getDataTimestamp()

        if (timestamp < 0) {
            throw new RuntimeException("Invalid negative timestamp.");
        }

        return timestamp;
    }
}

KStreamBuilder builder = new KStreamBuilder();
// set StreamTimestampExtractor explicitly for "streamInputTopic"
KStream stream = builder.stream(new StreamTimestampExtractor(), keySerde, valueSerde, "streamInputTopic");
KTable table= builder.table("tableInputTopic");

Properties props = new Properties(); // omitting mandatory configs for brevity

KafkaStreams streams = new KafkaStreams(builder, props);

KTable Changes

The following methods have been deprecated on the KTable interface

  • void foreach(final ForeachAction<? super K, ? super V> action)
  • void print()
  • void print(final String streamName)
  • void print(final Serde<K> keySerde, final Serde<V> valSerde)
  • void print(final Serde<K> keySerde, final Serde<V> valSerde, final String streamName)
  • void writeAsText(final String filePath)
  • void writeAsText(final String filePath, final Serde<K> keySerde, final Serde<V> valSerde)
  • void writeAsText(final String filePath, final String streamName)
  • void writeAsText(final String filePath, final String streamName, final Serde<K> keySerde, final Serde<V> valSerde)

These methods have been deprecated in favor of using the Interactive Queries API.

If you want to query the current content of the state store backing the KTable, use the following approach:

  • Make a call to KafkaStreams.store(String storeName, QueryableStoreType<T> queryableStoreType) followed by a call to ReadOnlyKeyValueStore.all() to iterate over the keys of a KTable.

If you want to view the changelog stream of the KTable then you could do something along the lines of the following:

  • Call KTable.toStream() then call KStream#print().

API changes (from Confluent Platform 3.1 to Confluent Platform 3.2)

Kafka Streams and its API were improved and modified since the release of Confluent Platform 3.1.x. Some of these changes are breaking changes that require you to update the code of your Kafka Streams applications. In this section we focus on only these breaking changes.

Handling Negative Timestamps and Timestamp Extractor Interface

Kafka Streams behavior with regard to invalid (i.e., negative) timestamps was improved. By default you will still get an exception on an invalid timestamp. However, you can reconfigure your application to react more gracefully to invalid timestamps which was not possible before.

Even if you do not use a custom timestamp extractor, you need to recompile your application code, because the TimestampExtractor interface was changed in an incompatible way.

The internal behavior of Kafka Streams with regard to negative timestamps was changed. Instead of raising an exception if the timestamp extractor returns a negative timestamp, the corresponding record will be dropped silently and not be processed. This allows to process topic for which only a few records cannot provide a valid timestamp. Furthermore, the TimestampExtractor interface was changed and now has one additional parameter. This parameter provides a timestamp that can be used, for example, to return an estimated timestamp, if no valid timestamp can be extracted from the current record.

The old default timestamp extractor ConsumerRecordTimestampExtractor was replaced with FailOnInvalidTimestamp, and two new extractors which both extract a record’s built-in timestamp were added (LogAndSkipOnInvalidTimestamp and UsePreviousTimeOnInvalidTimestamp). The new default extractor (FailOnInvalidTimestamp) raises an exception in case of a negative built-in record timestamp such that Kafka Streams’ default behavior is kept (i.e., fail-fast on negative timestamp). The two newly added extractors allow to handle negative timestamp more gracefully by implementing a log-and-skip and timestamp-estimation strategy.

// old interface
public class TimestampExtractor {
  // returning -1 results in an exception
  long extract(ConsumerRecord<Object, Object> record);
}

// new interface
public class TimestampExtractor {
  // provides a timestamp that could be used as a timestamp estimation,
  // if no valid timestamp can be extracted from the current record
  //
  // allows to return -1, which tells Kafka Streams to not process the record (it will be dropped silently)
  long extract(ConsumerRecord<Object, Object> record, long previousTimestamp);
}

Metrics

If you provide custom metrics by implementing interface StreamsMetrics you need to update your code as the interface has many new methods allowing to register finer grained metrics than before. More details are available in KIP-114.

// old interface
public interface StreamsMetrics {
  // Add the latency sensor.
  Sensor addLatencySensor(String scopeName, String entityName, String operationName, String... tags);

  // Record the given latency value of the sensor.
  void recordLatency(Sensor sensor, long startNs, long endNs);
}

// new interface
public interface StreamsMetrics {
  // Get read-only handle on global metrics registry.
  Map<MetricName, ? extends Metric> metrics();

  // Add a latency and throughput sensor for a specific operation
  Sensor addLatencyAndThroughputSensor(final String scopeName,
                                       final String entityName,
                                       final String operationName,
                                       final Sensor.RecordingLevel recordingLevel,
                                       final String... tags);

  // Record the given latency value of the sensor.
  void recordLatency(final Sensor sensor,
                     final long startNs,
                     final long endNs);

  // Add a throughput sensor for a specific operation:
  Sensor addThroughputSensor(final String scopeName,
                             final String entityName,
                             final String operationName,
                             final Sensor.RecordingLevel recordingLevel,
                             final String... tags);

  // Record the throughput value of a sensor.
  void recordThroughput(final Sensor sensor,
                        final long value);

  // Generic method to create a sensor.
  Sensor addSensor(final String name,
                   final Sensor.RecordingLevel recordingLevel);

  // Generic method to create a sensor with parent sensors.
  Sensor addSensor(final String name,
                   final Sensor.RecordingLevel recordingLevel,
                   final Sensor... parents);

  // Remove a sensor.
  void removeSensor(final Sensor sensor);
}

Scala

Starting with 0.10.2.0, if your application is written in Scala, you may need to declare types explicitly in order for the code to compile. The StreamToTableJoinScalaIntegrationTest has an example where the types of return variables are explicitly declared.

API changes (from Confluent Platform 3.0 to Confluent Platform 3.1)

Stream grouping and aggregation

Grouping (i.e., repartitioning) and aggregation of the KStream API was significantly changed to be aligned with the KTable API. Instead of using a single method with many parameters, grouping and aggregation is now split into two steps. First, a KStream is transformed into a KGroupedStream that is a repartitioned copy of the original KStream. Afterwards, an aggregation can be performed on the KGroupedStream, resulting in a new KTable that contains the result of the aggregation.

Thus, the methods KStream#aggregateByKey(...), KStream#reduceByKey(...), and KStream#countByKey(...) were replaced by KStream#groupBy(...) and KStream#groupByKey(...) which return a KGroupedStream. While KStream#groupByKey(...) groups on the current key, KStream#groupBy(...) sets a new key and re-partitions the data to build groups on the new key. The new class KGroupedStream provides the corresponding methods aggregate(...), reduce(...), and count(...).

KStream stream = builder.stream(...);
Reducer reducer = new Reducer() { /* ... */ };

// old API
KTable newTable = stream.reduceByKey(reducer, name);

// new API, Group by existing key
KTable newTable = stream.groupByKey().reduce(reducer, name);
// or Group by a different key
KTable otherTable = stream.groupBy((key, value) -> value).reduce(reducer, name);

Auto Repartitioning

Previously when performing KStream#join(...), KStream#outerJoin(...) or KStream#leftJoin(...) operations after a key changing operation, i.e, KStream#map(...), KStream#flatMap(...), KStream#selectKey(...) the developer was required to call KStream#through(...) to repartition the mapped KStream This is no longer required. Repartitioning now happens automatically for all join operations.

KStream streamOne = builder.stream(...);
KStream streamTwo = builder.stream(...);
KeyValueMapper selector = new KeyValueMapper() { /* ... */ };
ValueJoiner joiner = new ValueJoiner { /* ... */ };
JoinWindows windows = JoinWindows.of("the-join").within(60 * 1000);

// old API
KStream oldJoined = streamOne.selectKey(selector)
                             .through("repartitioned-topic")
                             .join(streamTwo,
                                   joiner,
                                   windows);

// new API
KStream newJoined = streamOne.selectKey((key,value) -> value)
                             .join(streamTwo,
                                   joiner,
                                   windows);

TopologyBuilder

Two public method signatures have been changed on TopologyBuilder, TopologyBuilder#sourceTopics(String applicationId) and TopologyBuilder#topicGroups(String applicationId). These methods no longer take applicationId as a parameter and instead you should call TopologyBuilder#setApplicationId(String applicationId) before calling one of these methods.

TopologyBuilder builder = new TopologyBuilder();
...

// old API
Set<String> topics = topologyBuilder.sourceTopics("applicationId");
Map<Integer, TopicsInfo> topicGroups = topologyBuilder.topicGroups("applicationId");

// new API
topologyBuilder.setApplicationId("applicationId");
Set<String> topics = topologyBuilder.sourceTopics();
Map<Integer, TopicsInfo> topicGroups = topologyBuilder.topicGroups();

DSL: New parameters to specify state store names

Apache Kafka 0.10.1 introduces Interactive Queries, which allow you to directly query state stores of a Kafka Streams application. This new feature required a few changes to the operators in the DSL. Starting with Kafka 0.10.1, state stores must be always be “named”, which includes both explicitly used state stores (e.g., defined by the user) and internally used state stores (e.g., created behind the scenes by operations such as count()). This naming is a prerequisite to make state stores queryable. As a result of this, the previous “operator name” is now the state store name. This change affects KStreamBuilder#table(...) and windowed aggregates KGroupedStream#count(...), #reduce(...), and #aggregate(...).

// old API
builder.table("topic");
builder.table(keySerde, valSerde, "topic");

table2 = table1.through("topic");

stream.countByKey(TimeWindows.of("windowName", 1000)); // window has a name

// new API
builder.table("topic", "storeName"); // requires to provide a store name to make KTable queryable
builder.table(keySerde, valSerde, "topic", "storeName"); // requires to provide a store name to make KTable queryable

table2 = table1.through("topic", "storeName"); // requires to provide a store name to make KTable queryable

// for changes of countByKey() -> groupByKey().count(...), please see example above
// for changes of TimeWindows.of(...), please see example below
stream.groupByKey().count(TimeWindows.of(1000), "countStoreName"); // window name removed, store name added

Windowing

The API for JoinWindows was improved. It is not longer possible to define a window with a default size (of zero). Furthermore, windows are not named anymore. Rather, any such naming is now done for state stores. See section DSL: New parameters to specify state store names above).

// old API
JoinWindows.of("name"); // defines window with size zero
JoinWindows.of("name").within(60 * 1000L);

TimeWindows.of("name", 60 * 1000L);
UnlimitedWindows.of("name", 60 * 1000L);

// new API, no name, requires window size
JoinWindows.of(0); // no name; set window size explicitly to zero
JoinWindows.of(60 * 1000L); // no name

TimeWindows.of(60 * 1000L); // not required to specify a name anymore
UnlimitedWindows.of(); // not required to specify a name anymore