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spark-sql-streaming-KafkaSourceProvider.adoc

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KafkaSourceProvider — Data Source Provider for Apache Kafka

KafkaSourceProvider is a streaming data source provider for KafkaSource (that is both the batch and streaming data source for Apache Kafka).

KafkaSourceProvider (as a DataSourceRegister) is registered as kafka format.

spark.readStream.format("kafka")

KafkaSourceProvider requires the following options (that you can set using option method of DataStreamReader or DataStreamWriter):

  1. Exactly one option for subscribe, subscribepattern or assign

  2. kafka.bootstrap.servers (that becomes bootstrap.servers property of the Kafka client)

Tip
 Refer to KafkaSource’s Options for the supported options.
Note
 endingoffsets option is not allowed in streaming queries.
Note
 KafkaSourceProvider is part of spark-sql-kafka-0-10 Library Dependency and so has to be "installed" in spark-shell using --package command-line option. 
// See the section about KafkaSource for a complete example
val records = spark.
  readStream.
  format("kafka").  // <-- use KafkaSourceProvider
  option("subscribe", "raw-events").
  option("kafka.bootstrap.servers", "localhost:9092").
  option("startingoffsets", "earliest").
  option("maxOffsetsPerTrigger", 1).
  load

Creating KafkaSource — createSource Method

createSource(
  sqlContext: SQLContext,
  metadataPath: String,
  schema: Option[StructType],
  providerName: String,
  parameters: Map[String, String]): Source

Internally, createSource first validates stream options.

Caution
 FIXME
Note
 createSource is a part of StreamSourceProvider Contract to create a streaming source for kafka format.

spark-sql-kafka-0-10 Library Dependency

The new structured streaming API for Kafka is part of the spark-sql-kafka-0-10 artifact. Add the following dependency to sbt project to use the streaming integration:

libraryDependencies += "org.apache.spark" %% "spark-sql-kafka-0-10" % "2.2.0"
Tip

spark-sql-kafka-0-10 module is not included in the CLASSPATH of spark-shell so you have to start it with --packages command-line option.

./bin/spark-shell --packages org.apache.spark:spark-sql-kafka-0-10_2.11:2.2.0
Note
 Replace 2.2.0 or 2.3.0-SNAPSHOT with one of the available versions found at The Central Repository’s Search that matches your version of Spark.

Validating General Options For Batch And Streaming Queries — validateGeneralOptions Internal Method

validateGeneralOptions(parameters: Map[String, String]): Unit
Note
 Parameters are case-insensitive, i.e. OptioN and option are equal.

validateGeneralOptions makes sure that exactly one topic subscription strategy is used in parameters and can be:

  • subscribe

  • subscribepattern

  • assign

validateGeneralOptions reports an IllegalArgumentException when there is no subscription strategy in use or there are more than one strategies used.

validateGeneralOptions makes sure that the value of subscription strategies meet the requirements:

  • assign strategy starts with { (the opening curly brace)

  • subscribe strategy has at least one topic (in a comma-separated list of topics)

  • subscribepattern strategy has the pattern defined

validateGeneralOptions makes sure that group.id has not been specified and reports an IllegalArgumentException otherwise.

Kafka option 'group.id' is not supported as user-specified consumer groups are not used to track offsets.

validateGeneralOptions makes sure that auto.offset.reset has not been specified and reports an IllegalArgumentException otherwise.

Kafka option 'auto.offset.reset' is not supported.
Instead set the source option 'startingoffsets' to 'earliest' or 'latest' to specify where to start. Structured Streaming manages which offsets are consumed internally, rather than relying on the kafkaConsumer to do it. This will ensure that no data is missed when new topics/partitions are dynamically subscribed. Note that 'startingoffsets' only applies when a new Streaming query is started, and
that resuming will always pick up from where the query left off. See the docs for more details.

validateGeneralOptions makes sure that the following options have not been specified and reports an IllegalArgumentException otherwise:

  • kafka.key.deserializer

  • kafka.value.deserializer

  • kafka.enable.auto.commit

  • kafka.interceptor.classes

In the end, validateGeneralOptions makes sure that kafka.bootstrap.servers option was specified and reports an IllegalArgumentException otherwise.

Option 'kafka.bootstrap.servers' must be specified for configuring Kafka consumer
Note
 validateGeneralOptions is used when KafkaSourceProvider validates options for streaming and batch queries.

Creating ConsumerStrategy — strategy Internal Method

strategy(caseInsensitiveParams: Map[String, String])

Internally, strategy finds the keys in the input caseInsensitiveParams that are one of the following and creates a corresponding ConsumerStrategy.

Table 1. KafkaSourceProvider.strategy’s Key to ConsumerStrategy Conversion
Key ConsumerStrategy

assign

strategy uses JsonUtils.partitions method to parse a JSON with topic names and partitions, e.g.

{"topicA":[0,1],"topicB":[0,1]}

The topic names and partitions are mapped directly to Kafka’s TopicPartition objects.

subscribe

SubscribeStrategy with topic names

strategy extracts topic names from a comma-separated string, e.g.

topic1,topic2,topic3

subscribepattern

SubscribePatternStrategy with topic subscription regex pattern (that uses Java’s java.util.regex.Pattern for the pattern), e.g.

` topic\d `
Note

strategy is used when:

Specifying Name and Schema of Streaming Source for Kafka Format — sourceSchema Method

sourceSchema(
  sqlContext: SQLContext,
  schema: Option[StructType],
  providerName: String,
  parameters: Map[String, String]): (String, StructType)
Note
 sourceSchema is a part of StreamSourceProvider Contract to define the name and the schema of a streaming source.

sourceSchema gives the short name (i.e. kafka) and the fixed schema.

Internally, sourceSchema validates Kafka options and makes sure that the optional input schema is indeed undefined.

When the input schema is defined, sourceSchema reports a IllegalArgumentException.

Kafka source has a fixed schema and cannot be set with a custom one
Note
 sourceSchema is used exclusively when DataSource is requested the name and schema of a streaming source.

Validating Kafka Options for Streaming Queries — validateStreamOptions Internal Method

validateStreamOptions(caseInsensitiveParams: Map[String, String]): Unit

Firstly, validateStreamOptions makes sure that endingoffsets option is not used. Otherwise, validateStreamOptions reports a IllegalArgumentException.

ending offset not valid in streaming queries

validateStreamOptions then validates the general options.

Note
 validateStreamOptions is used when KafkaSourceProvider is requested the schema for Kafka source and to create a KafkaSource.