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KafkaWriteTask

KafkaWriteTask is used to <> (from a structured query) to Apache Kafka.

KafkaWriteTask is <> exclusively when KafkaWriter is requested to write the rows of a structured query to a Kafka topic.

KafkaWriteTask <> keys and values in their binary format (as JVM's bytes) and so uses the raw-memory unsafe row format only (i.e. UnsafeRow). That is supposed to save time for reconstructing the rows to very tiny JVM objects (i.e. byte arrays).

[[internal-properties]] .KafkaWriteTask's Internal Properties [cols="1m,2",options="header",width="100%"] |=== | Name | Description

| callback | [[callback]]

| failedWrite | [[failedWrite]]

| projection | [[projection]] UnsafeProjection

<> once when KafkaWriteTask is created. |===

=== [[execute]] Writing Rows to Kafka Asynchronously -- execute Method

[source, scala]

execute(iterator: Iterator[InternalRow]): Unit

execute uses Apache Kafka's Producer API to create a https://kafka.apache.org/0101/javadoc/index.html?org/apache/kafka/clients/producer/KafkaProducer.html[KafkaProducer] and https://kafka.apache.org/0101/javadoc/index.html?org/apache/kafka/clients/producer/KafkaProducer.html[ProducerRecord] for every row in iterator, and sends the rows to Kafka in batches asynchronously.

Internally, execute creates a KafkaProducer using Array[Byte] for the keys and values, and producerConfiguration for the producer's configuration.

NOTE: execute creates a single KafkaProducer for all rows.

For every row in the iterator, execute uses the internal <> to project (aka convert) InternalRow to an UnsafeRow object and take 0th, 1st and 2nd fields for a topic, key and value, respectively.

execute then creates a ProducerRecord and sends it to Kafka (using the KafkaProducer). execute registers a asynchronous Callback to monitor the writing.

[NOTE]

From https://kafka.apache.org/0101/javadoc/index.html?org/apache/kafka/clients/producer/KafkaProducer.html[KafkaProducer's documentation]:

> The send() method is asynchronous. When called it adds the record to a buffer of pending record sends and immediately returns. This allows the producer to batch together individual records for efficiency.

=== [[createProjection]] Creating UnsafeProjection -- createProjection Internal Method

[source, scala]

createProjection: UnsafeProjection

createProjection creates a UnsafeProjection with topic, key and value expressions/Expression.md[expressions] and the inputSchema.

createProjection makes sure that the following holds (and reports an IllegalStateException otherwise):

  • topic was defined (either as the input topic or in inputSchema) and is of type StringType
  • Optional key is of type StringType or BinaryType if defined
  • value was defined (in inputSchema) and is of type StringType or BinaryType

createProjection casts key and value expressions to BinaryType in UnsafeProjection.

NOTE: createProjection is used exclusively when KafkaWriteTask is created (as <>).

=== [[close]] close Method

[source, scala]

close(): Unit

close...FIXME

NOTE: close is used when...FIXME

=== [[creating-instance]] Creating KafkaWriteTask Instance

KafkaWriteTask takes the following when created:

  • [[producerConfiguration]] Kafka Producer configuration (as Map[String, Object])
  • [[inputSchema]] Input schema (as Seq[Attribute])
  • [[topic]] Topic name

KafkaWriteTask initializes the <>.


Last update: 2020-11-15