I have the following code
class Consumer(val consumer: KafkaConsumer<String, ConsumerRecord<String>>) {
fun run() {
consumer.seekToEnd(emptyList())
val pollDuration = 30 // seconds
while (true) {
val records = consumer.poll(Duration.ofSeconds(pollDuration))
// perform record analysis and commitSync()
}
}
}
}
The topic which the consumer is subscribed to continously receives records. Occasionally, the consumer will crash due to the processing step. When the consumer then is restarted, I want it to consume from the latest offset on the topic (i.e. ignore records that were published to the topic while the consumer was down). I thought the seekToEnd() method would ensure that. However, it seems like the method has no effect at all. The consumer starts to consume from the offset from which it crashed.
What is the correct way to use seekToEnd()?
Edit: The consumer is created with the following configs
fun <T> buildConsumer(valueDeserializer: String): KafkaConsumer<String, T> {
val props = setupConfig(valueDeserializer)
Common.setupConsumerSecurityProtocol(props)
return createConsumer(props)
}
fun setupConfig(valueDeserializer: String): Properties {
// Configuration setup
val props = Properties()
props[ConsumerConfig.GROUP_ID_CONFIG] = config.applicationId
props[ConsumerConfig.CLIENT_ID_CONFIG] = config.kafka.clientId
props[ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG] = config.kafka.bootstrapServers
props[AbstractKafkaSchemaSerDeConfig.SCHEMA_REGISTRY_URL_CONFIG] = config.kafka.schemaRegistryUrl
props[ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG] = config.kafka.stringDeserializer
props[ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG] = valueDeserializer
props[KafkaAvroDeserializerConfig.SPECIFIC_AVRO_READER_CONFIG] = "true"
props[ConsumerConfig.MAX_POLL_INTERVAL_MS_CONFIG] = config.kafka.maxPollIntervalMs
props[ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG] = config.kafka.sessionTimeoutMs
props[ConsumerConfig.ALLOW_AUTO_CREATE_TOPICS_CONFIG] = "false"
props[ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG] = "false"
props[ConsumerConfig.AUTO_OFFSET_RESET_CONFIG] = "latest"
return props
}
fun <T> createConsumer(props: Properties): KafkaConsumer<String, T> {
val consumer = KafkaConsumer<String, T>(props)
consumer.subscribe(listOf(config.kafka.inputTopic))
return consumer
}
I found a solution!
I needed to add a dummy poll as a part of the consumer initialization process. Since several Kafka methods are evaluated lazily, it is necessary with a dummy poll to assign partitions to the consumer. Without the dummy poll, the consumer tries to seek to the end of partitions that are null. As a result, seekToEnd() has no effect.
It is important that the dummy poll duration is long enough for the partitions to get assigned. For instance with consumer.poll((Duration.ofSeconds(1)), the partitions did not get time to be assigned before the program moved on to the next method call (i.e. seekToEnd()).
Working code could look something like this
class Consumer(val consumer: KafkaConsumer<String, ConsumerRecord<String>>) {
fun run() {
// Initialization
val pollDuration = 30 // seconds
consumer.poll((Duration.ofSeconds(pollDuration)) // Dummy poll to get assigned partitions
// Seek to end and commit new offset
consumer.seekToEnd(emptyList())
consumer.commitSync()
while (true) {
val records = consumer.poll(Duration.ofSeconds(pollDuration))
// perform record analysis and commitSync()
}
}
}
}
The seekToEnd method requires the information on the actual partition (in Kafka terms TopicPartition) on which you plan to make your consumer read from the end.
I am not familiar with the Kotlin API, but checking the JavaDocs on the KafkaConsumer's method seekToEnd you will see, that it asks for a collection of TopicPartitions.
As you are currently using emptyList(), it will have no impact at all, just like you observed.