Class: Kafka::FetchOperation

Inherits:
Object
  • Object
show all
Defined in:
lib/kafka/fetch_operation.rb

Overview

Fetches messages from one or more partitions.

operation = Kafka::FetchOperation.new(
  cluster: cluster,
  logger: logger,
  min_bytes: 1,
  max_wait_time: 10,
)

# These calls will schedule fetches from the specified topics/partitions.
operation.fetch_from_partition("greetings", 42, offset: :latest, max_bytes: 100000)
operation.fetch_from_partition("goodbyes", 13, offset: :latest, max_bytes: 100000)

operation.execute

Instance Method Summary collapse

Constructor Details

#initialize(cluster:, logger:, min_bytes: 1, max_bytes: 10485760, max_wait_time: 5) ⇒ FetchOperation

Returns a new instance of FetchOperation.



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# File 'lib/kafka/fetch_operation.rb', line 24

def initialize(cluster:, logger:, min_bytes: 1, max_bytes: 10485760, max_wait_time: 5)
  @cluster = cluster
  @logger = TaggedLogger.new(logger)
  @min_bytes = min_bytes
  @max_bytes = max_bytes
  @max_wait_time = max_wait_time
  @topics = {}

  @offset_resolver = Kafka::FetchedOffsetResolver.new(
    logger: logger
  )
end

Instance Method Details

#execute ⇒ Object 



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# File 'lib/kafka/fetch_operation.rb', line 51

def execute
  @cluster.add_target_topics(@topics.keys)
  @cluster.refresh_metadata_if_necessary!

  topics_by_broker = {}

  if @topics.none? {|topic, partitions| partitions.any? }
    raise NoPartitionsToFetchFrom
  end

  @topics.each do |topic, partitions|
    partitions.each do |partition, options|
      broker = @cluster.get_leader(topic, partition)

      topics_by_broker[broker] ||= {}
      topics_by_broker[broker][topic] ||= {}
      topics_by_broker[broker][topic][partition] = options
    end
  end

  topics_by_broker.flat_map do |broker, topics|
    @offset_resolver.resolve!(broker, topics)

    options = {
      max_wait_time: @max_wait_time * 1000, # Kafka expects ms, not secs
      min_bytes: @min_bytes,
      max_bytes: @max_bytes,
      topics: topics,
    }

    response = broker.fetch_messages(**options)

    response.topics.flat_map do |fetched_topic|
      fetched_topic.partitions.map do |fetched_partition|
        begin
          Protocol.handle_error(fetched_partition.error_code)
        rescue Kafka::OffsetOutOfRange => e
          e.topic = fetched_topic.name
          e.partition = fetched_partition.partition
          e.offset = topics.fetch(e.topic).fetch(e.partition).fetch(:fetch_offset)

          raise e
        rescue Kafka::Error => e
          topic = fetched_topic.name
          partition = fetched_partition.partition
          @logger.error "Failed to fetch from #{topic}/#{partition}: #{e.message}"
          raise e
        end

        Kafka::FetchedBatchGenerator.new(
          fetched_topic.name,
          fetched_partition,
          topics.fetch(fetched_topic.name).fetch(fetched_partition.partition).fetch(:fetch_offset),
          logger: @logger
        ).generate
      end
    end
  end
rescue Kafka::ConnectionError, Kafka::LeaderNotAvailable, Kafka::NotLeaderForPartition
  @cluster.mark_as_stale!

  raise
end

#fetch_from_partition(topic, partition, offset: :latest, max_bytes: 1048576) ⇒ Object 



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# File 'lib/kafka/fetch_operation.rb', line 37

def fetch_from_partition(topic, partition, offset: :latest, max_bytes: 1048576)
  if offset == :earliest
    offset = -2
  elsif offset == :latest
    offset = -1
  end

  @topics[topic] ||= {}
  @topics[topic][partition] = {
    fetch_offset: offset,
    max_bytes: max_bytes,
  }
end