[BEAM-990] KafkaIO does not commit offsets to Kafka

• Type: Bug
• Status: Open
• Priority: P3
• Resolution: Unresolved
• Component/s: io-java-kafka
• Labels: KafkaIO
• Assignee: Unassigned
• Reporter: Alban Perillat-Merceroz
• Created: 16/Nov/16 09:57
• Updated: 03/Jun/22 16:20

Description

I use KafkaIO as a source, and I would like consumed offsets to be stored in Kafka (in the __consumer_offsets topic).

I'm configuring the Kafka reader with

.updateConsumerProperties(ImmutableMap.of(
              ConsumerConfig.GROUP_ID_CONFIG, "my-group",
              ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, java.lang.Boolean.TRUE,
              ConsumerConfig.AUTO_COMMIT_INTERVAL_MS_CONFIG, "10" // doesn't work with default value either (5000ms)
            ))

But the offsets are not stored in Kafka (nothing in __consumer_offsets, next job will restart at latest offset).

I can't find in the code where the offsets are supposed to be committed.

I tried to add a manual commit in the consumerPollLoop() method, and it works, offsets are committed:

private void consumerPollLoop() {
            // Read in a loop and enqueue the batch of records, if any, to availableRecordsQueue
            while (!closed.get()) {
                try {
                    ConsumerRecords<byte[], byte[]> records = consumer.poll(KAFKA_POLL_TIMEOUT.getMillis());
                    if (!records.isEmpty() && !closed.get()) {
                        availableRecordsQueue.put(records); // blocks until dequeued.
                        // Manual commit
                        consumer.commitSync();
                    }
                } catch (InterruptedException e) {
                    LOG.warn("{}: consumer thread is interrupted", this, e); // not expected
                    break;
                } catch (WakeupException e) {
                    break;
                }
            }

            LOG.info("{}: Returning from consumer pool loop", this);
        }

Is this a bug in KafkaIO or am I misconfiguring something?

Disclamer: I'm currently using KafkaIO in Dataflow, using the backport in Dataflow SDK (https://github.com/GoogleCloudPlatform/DataflowJavaSDK/blob/master/contrib/kafka/src/main/java/com/google/cloud/dataflow/contrib/kafka/KafkaIO.java), but I'm confident the code is similar for this case.

Edit: I found the correct method where KafkaIO is supposed to commit at the end of a batch. I'm currently testing it and will be able to open a pull request soon:

// KafkaCheckpointMark.java

    /**
     * Optional consumer that will be used to commit offsets into Kafka when finalizeCheckpoint() is called
     */
    @Nullable
    private final Consumer consumer;

    public KafkaCheckpointMark(List<PartitionMark> partitions, @Nullable Consumer consumer) {
        this.partitions = partitions;
        this.consumer = consumer;
    }

    /**
     * Commit synchronously into Kafka offsets that have been passed downstream.
     */
    @Override
    public void finalizeCheckpoint() throws IOException {
        if (consumer == null) {
            LOG.warn("finalizeCheckpoint(): no consumer provided, will not commit anything.");
            return;
        }
        if (partitions.size() == 0) {
            LOG.info("finalizeCheckpoint(): nothing to commit to Kafka.");
            return;
        }

        final Map<TopicPartition, OffsetAndMetadata> offsets = newHashMap();
        String committedOffsets = "";
        for (PartitionMark partition : partitions) {
            TopicPartition topicPartition = partition.getTopicPartition();
            offsets.put(topicPartition, new OffsetAndMetadata(partition.offset));
            committedOffsets += topicPartition.topic() + "-" + topicPartition.partition() + ":" + partition.offset + ",";
        }

        final String printableOffsets = committedOffsets.substring(0, committedOffsets.length() - 1);
        try {
            consumer.commitSync(offsets);
            LOG.info("finalizeCheckpoint(): committed Kafka offsets {}", printableOffsets);
        } catch (Exception e) {
            LOG.error("finalizeCheckpoint(): {} when trying to commit Kafka offsets [{}]",
                    e.getClass().getSimpleName(),
                    printableOffsets);
        }
    }