Module: Karafka::Processing::Strategies::Dlq

Includes:
Default
Included in:
DlqMom
Defined in:
lib/karafka/processing/strategies/dlq.rb

Overview

When using dead letter queue, processing won’t stop after defined number of retries upon encountering non-critical errors but the messages that error will be moved to a separate topic with their payload and metadata, so they can be handled differently.

Constant Summary collapse

FEATURES =

Apply strategy when only dead letter queue is turned on

%i[
  dead_letter_queue
].freeze

Instance Method Summary collapse

Methods included from Default

#commit_offsets, #commit_offsets!, #handle_before_consume, #handle_consume, #handle_eofed, #handle_idle, #handle_revoked, #handle_shutdown

Methods included from Base

#handle_before_consume, #handle_consume, #handle_idle, #handle_revoked, #handle_shutdown

Instance Method Details

#dispatch_to_dlq(skippable_message) ⇒ Object

Moves the broken message into a separate queue defined via the settings

Parameters:



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# File 'lib/karafka/processing/strategies/dlq.rb', line 112

def dispatch_to_dlq(skippable_message)
  producer.public_send(
    topic.dead_letter_queue.dispatch_method,
    topic: topic.dead_letter_queue.topic,
    payload: skippable_message.raw_payload
  )

  # Notify about dispatch on the events bus
  Karafka.monitor.instrument(
    'dead_letter_queue.dispatched',
    caller: self,
    message: skippable_message
  )
end

#find_skippable_message ⇒ Array<Karafka::Messages::Message, Boolean>

Finds the message may want to skip (all, starting from first)

Returns:

  • (Array<Karafka::Messages::Message, Boolean>) —

    message we may want to skip and information if this message was from marked offset or figured out via mom flow



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# File 'lib/karafka/processing/strategies/dlq.rb', line 96

def find_skippable_message
  skippable_message = messages.find do |msg|
    coordinator.marked? && msg.offset == coordinator.seek_offset
  end

  # If we don't have the message matching the last comitted offset, it means that
  # user operates with manual offsets and we're beyond the batch in which things
  # broke for the first time. Then we skip the first (as no markings) and we
  # move on one by one.
  skippable_message ? [skippable_message, true] : [messages.first, false]
end

#handle_after_consume ⇒ Object

When manual offset management is on, we do not mark anything as consumed automatically and we rely on the user to figure things out



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# File 'lib/karafka/processing/strategies/dlq.rb', line 55

def handle_after_consume
  return if revoked?

  if coordinator.success?
    coordinator.pause_tracker.reset

    return if coordinator.manual_pause?

    mark_as_consumed(messages.last)
  elsif coordinator.pause_tracker.attempt <= topic.dead_letter_queue.max_retries
    retry_after_pause
  # If we've reached number of retries that we could, we need to skip the first message
  # that was not marked as consumed, pause and continue, while also moving this message
  # to the dead topic
  else
    # We reset the pause to indicate we will now consider it as "ok".
    coordinator.pause_tracker.reset

    skippable_message, = find_skippable_message

    # Send skippable message to the dql topic
    dispatch_to_dlq(skippable_message)

    # We mark the broken message as consumed and move on
    if mark_after_dispatch?
      mark_dispatched_to_dlq(skippable_message)

      return if revoked?
    else
      coordinator.seek_offset = skippable_message.offset + 1
    end

    # We pause to backoff once just in case.
    pause(coordinator.seek_offset, nil, false)
  end
end

#mark_after_dispatch? ⇒ Boolean

Returns should we mark given message as consumed after dispatch. For default non MOM strategies if user did not explicitly tell us not to, we mark it. Default is nil, which means true in this case. If user provided alternative value, we go with it.

Returns:

  • (Boolean) —

    should we mark given message as consumed after dispatch. For default non MOM strategies if user did not explicitly tell us not to, we mark it. Default is nil, which means true in this case. If user provided alternative value, we go with it.



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# File 'lib/karafka/processing/strategies/dlq.rb', line 131

def mark_after_dispatch?
  return true if topic.dead_letter_queue.mark_after_dispatch.nil?

  topic.dead_letter_queue.mark_after_dispatch
end

#mark_as_consumed(message) ⇒ Object

Override of the standard #mark_as_consumed in order to handle the pause tracker reset in case DLQ is marked as fully independent. When DLQ is marked independent, any offset marking causes the pause count tracker to reset. This is useful when the error is not due to the collective batch operations state but due to intermediate “crawling” errors that move with it

Parameters:

See Also:

  • for more details


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# File 'lib/karafka/processing/strategies/dlq.rb', line 25

def mark_as_consumed(message)
  # If we are not retrying pause count is already 0, no need to try to reset the state
  return super unless retrying?
  # If we do not use independent marking on DLQ, we just mark as consumed
  return super unless topic.dead_letter_queue.independent?
  # If we were not able to mark no need to reset
  return false unless super

  coordinator.pause_tracker.reset

  true
end

#mark_as_consumed!(message) ⇒ Object

Override of the standard #mark_as_consumed!. Resets the pause tracker count in case DLQ was configured with the independent flag.

Parameters:

See Also:

  • for more details


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# File 'lib/karafka/processing/strategies/dlq.rb', line 43

def mark_as_consumed!(message)
  return super unless retrying?
  return super unless topic.dead_letter_queue.independent?
  return false unless super

  coordinator.pause_tracker.reset

  true
end

#mark_dispatched_to_dlq(skippable_message) ⇒ Object

Marks message that went to DLQ (if applicable) based on the requested method

Parameters:



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# File 'lib/karafka/processing/strategies/dlq.rb', line 139

def mark_dispatched_to_dlq(skippable_message)
  case topic.dead_letter_queue.marking_method
  when :mark_as_consumed
    mark_as_consumed(skippable_message)
  when :mark_as_consumed!
    mark_as_consumed!(skippable_message)
  else
    # This should never happen. Bug if encountered. Please report
    raise Karafka::Errors::UnsupportedCaseError
  end
end