Why commitAsync fails to commit the first 2 offsets

问题

I faced a weird problem at which the consumer can not make comitAsync the first 2 offsets of the log and i don't know the reason. It is very weird because the other messages at the same asynchronous send of the producer received and commited succesfuly by the consumer .Can someone find the source of this problem.. I quote my code below and an output example

package com.panos.example;

import kafka.utils.ShutdownableThread;
import org.apache.kafka.clients.consumer.*;

import org.apache.kafka.common.TopicPartition;

import java.util.Collections;
import java.util.Map;
import java.util.Properties;

public class Consumer extends ShutdownableThread {
    private final KafkaConsumer<Integer, String> consumer;
    private final String topic;

    public Consumer(String topic) {
        super("KafkaConsumerExample", false);
        Properties props = new Properties();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "192.168.1.75:9092");
        props.put(ConsumerConfig.GROUP_ID_CONFIG, "DemoConsumer");
        props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, "false");
        props.put(ConsumerConfig.AUTO_COMMIT_INTERVAL_MS_CONFIG, "1000");
        props.put(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG, "30000");
        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.IntegerDeserializer");
        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringDeserializer");

        consumer = new KafkaConsumer<Integer, String>(props);
        this.topic = topic;
    }

    @Override
    public void doWork() {

        consumer.subscribe(Collections.singletonList(this.topic));
        try {
            ConsumerRecords<Integer, String> records = consumer.poll(1000);
            long startTime = System.currentTimeMillis();
            if (!records.isEmpty()) {
                System.out.println("C : {} Total No. of records received : {}" + records.count());

                for (ConsumerRecord<Integer, String> record : records) {
                    System.out.println("Received message: (" + record.key() + ", " + record.value() + ") at offset " + record.offset());
                    consumer.commitAsync(new ConsumerCallBack(startTime,record.value(), record.offset()));
                }

            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public String name() {
        return null;
    }

    @Override
    public boolean isInterruptible() {
        return false;
    }


    class ConsumerCallBack implements OffsetCommitCallback {

        private final long startTime;
        private String message;
        private final String NewLine = System.getProperty("line.separator");
        private long offset;

        public ConsumerCallBack(long startTime) {
            this.startTime = startTime;
        }

        public ConsumerCallBack(long startTime, String message, long offset) {
            this.startTime = startTime;
            this.message=message;
            this.offset = offset;
        }

        public void onComplete(Map<TopicPartition, OffsetAndMetadata> CurrentOffset,
                               Exception exception) {
            long elapsedTime = System.currentTimeMillis() - startTime;
            if (exception != null) {
                System.out.println("Message : {" + message + "}, committed successfully at offset " + offset +
                        CurrentOffset + "elapsed time :" + elapsedTime);
            } else {
                System.out.println(exception.toString());
               /* JOptionPane.showMessageDialog(new Frame(),
                        "Something Goes Wrong with the Server Please Try again Later.",
                        "Inane error",
                        JOptionPane.ERROR_MESSAGE);*/
            }
        }
    }
}

As you can see all message committed successfully except the first 2 without any exception. Why this happens?

Received message: (1, Message_1) at offset 160
Received message: (2, Message_2) at offset 161
Received message: (3, Message_3) at offset 162
Received message: (4, Message_4) at offset 163
Message : {Message_3}, committed successfully at offset 162{test-0=OffsetAndMetadata{offset=164, metadata=''}}elapsed time :6
Message : {Message_4}, committed successfully at offset 163{test-0=OffsetAndMetadata{offset=164, metadata=''}}elapsed time :6

回答1:

If you use commitAsync it can happen that multiple commits are squashed together into a single commit message. As offsets are committed in increasing order, a commit of offset X is an implicit commit for all offsets that are smaller than X. In your case, it seems, that the commits or the first three offsets are done my a single commit of offset 3.

来源：https://stackoverflow.com/questions/37794718/why-commitasync-fails-to-commit-the-first-2-offsets