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From: chinmaykolhatkar <git@git.apache.org>
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References: <git-pr-298-apex-malhar@git.apache.org>
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Subject: [GitHub] apex-malhar pull request #298: *For review only* [APEXMALHAR-2086] Kafka out...
Content-Type: text/plain
Message-Id: <20160609002706.3DD9BDFF68@git1-us-west.apache.org>
Date: Thu,  9 Jun 2016 00:27:06 +0000 (UTC)
archived-at: Thu, 09 Jun 2016 00:27:12 -0000

Github user chinmaykolhatkar commented on a diff in the pull request:

    https://github.com/apache/apex-malhar/pull/298#discussion_r66365356
  
    --- Diff: kafka/src/main/java/org/apache/apex/malhar/kafka/AbstractExactlyOnceKafkaOutputOperator.java ---
    @@ -0,0 +1,385 @@
    +/**
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
    + *
    + *   http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing,
    + * software distributed under the License is distributed on an
    + * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    + * KIND, either express or implied.  See the License for the
    + * specific language governing permissions and limitations
    + * under the License.
    + */
    +
    +package org.apache.apex.malhar.kafka;
    +
    +import java.io.IOException;
    +import java.util.ArrayList;
    +import java.util.HashMap;
    +import java.util.HashSet;
    +import java.util.List;
    +import java.util.Map;
    +import java.util.Properties;
    +import java.util.Set;
    +import java.util.concurrent.ExecutionException;
    +
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +import org.apache.apex.malhar.lib.wal.FSWindowDataManager;
    +import org.apache.apex.malhar.lib.wal.WindowDataManager;
    +
    +import org.apache.kafka.clients.consumer.ConsumerRecord;
    +import org.apache.kafka.clients.consumer.ConsumerRecords;
    +import org.apache.kafka.clients.consumer.KafkaConsumer;
    +import org.apache.kafka.clients.producer.ProducerRecord;
    +import org.apache.kafka.common.PartitionInfo;
    +import org.apache.kafka.common.TopicPartition;
    +
    +import com.datatorrent.api.Context;
    +import com.datatorrent.api.DefaultInputPort;
    +import com.datatorrent.api.Operator;
    +
    +//       1. JavaDoc
    +//       2. Unit Test
    +//       3. Comparator -- not required
    +//       4. Generic Type
    +//       5. remove e.printStackTrace()
    +//       6. Should the Consumer be kept open?
    +
    +/**
    + * This is a base implementation of a Kafka output operator,
    + * which, in most cases, guarantees to send tuples to Kafka MQ only once.&nbsp;
    + * Subclasses should implement the methods for converting tuples into a format appropriate for Kafka.
    + * <p>
    + * Assuming messages kept in kafka are ordered by either key or value or keyvalue pair
    + * (For example, use timestamps as key), this Kafka OutputOperator always retrieve the last message from MQ as initial offset.
    + *  So that replayed message wouldn't be sent to kafka again.
    + *
    + * This is not "perfect exact once" in 2 cases:
    + * 1 Multiple producers produce messages to same kafka partition
    + * 2 You have same message sent out and before kafka synchronized this message among all the brokers, the operator is
    + * started again.
    + *
    + * <br>
    + * Ports:<br>
    + * <b>Input</b>: One input port<br>
    + * <b>Output</b>: No output port<br>
    + * <br>
    + * Properties:<br>
    + * configProperties<br>
    + * <br>
    + * Compile time checks:<br>
    + * Class derived from has to implement 2 methods:<br>
    + * tupleToKeyValue() to convert input tuples to kafka key value objects<br>
    + * compareToLastMsg() to compare incoming tuple with the last received msg in kafka so that the operator could skip the received ones<br>
    + * <br>
    + * Run time checks:<br>
    + * None<br>
    + * <br>
    + * Benchmarks:<br>
    + * TBD<br>
    + * </p>
    + *
    + * @displayName Abstract Exactly Once Kafka Output(0.9.0)
    + * @category Messaging
    + * @tags output operator
    + *
    + * @since 3.5
    + */
    +public abstract class AbstractExactlyOnceKafkaOutputOperator<T> extends AbstractKafkaOutputOperator<String, T>
    +    implements Operator.CheckpointNotificationListener
    +{
    +  private WindowDataManager windowDataManager = new FSWindowDataManager();
    +  private String key;
    +  private Integer operatorId;
    +  private String appId;
    +  private transient Long windowId;
    +  private transient Set<T> recoveredTuples = new HashSet<>();
    +  private int KAFKA_CONNECT_ATTEMPT = 10;
    +
    +  @Override
    +  public void setup(Context.OperatorContext context)
    +  {
    +    super.setup(context);
    +    this.operatorId = context.getId();
    +    this.windowDataManager.setup(context);
    +    this.appId = context.getValue(Context.DAGContext.APPLICATION_ID);
    +    this.key = appId + '#' + (new Integer(operatorId));
    +  }
    +
    +  @Override
    +  public void beginWindow(long windowId)
    +  {
    +    this.windowId = windowId;
    +
    +    if (windowId == windowDataManager.getLargestRecoveryWindow()) {
    +      rebuildLastWindow();
    +    }
    +  }
    +
    +  // Only the tuples in the incomplete window needs to be read from the Kafka.
    +  // Re-sent tuples from the previous windows are not written to Kafka.
    +  private void rebuildLastWindow()
    +  {
    +    recoveredTuples.clear();
    +
    +    Map<Integer,Long> storedOffsets = getStoredOffsets();
    +    Map<Integer,Long> currentOffsets = getCurrentOffsets();
    +
    +    if (storedOffsets == null || currentOffsets == null) {
    +      //TODO: Take some action
    +      return;
    +    }
    +
    +    KafkaConsumer consumer = KafkaConsumerInit();
    +
    +    List<TopicPartition> topicPartitions = new ArrayList<>();
    +
    +    for (Map.Entry<Integer,Long> entry: currentOffsets.entrySet()) {
    +
    +      topicPartitions.add(new TopicPartition(getTopic(), entry.getKey()));
    +    }
    +
    +    consumer.assign(topicPartitions);
    +
    +    // From each partitions in a topic
    +    // 1. Read the tuples between stored offset and the latest offset
    +    // 2. Check the Key to filter out the messages
    +    // 3. Store the recovered tuples in the HashSet
    +
    +    for (Map.Entry<Integer,Long> entry: currentOffsets.entrySet()) {
    +
    +      Long storedOffset = 0L;
    +      Integer currentPartition = entry.getKey();
    +      Long currentOffset = entry.getValue();
    +
    +      if (storedOffsets.containsKey(currentPartition)) {
    +        storedOffset = storedOffsets.get(currentPartition);
    +      }
    +
    +      if (storedOffset >= currentOffset) {
    +        continue;
    +      }
    +
    +      consumer.seek(new TopicPartition(getTopic(), currentPartition), storedOffset);
    +
    +      int kafkaAttempt = 0;
    +
    +      while ( true ) {
    +
    +        ConsumerRecords<String, String> consumerRecords = consumer.poll(100);
    +
    +        if (consumerRecords.count() == 0) {
    +          ++kafkaAttempt;
    +
    +          if (kafkaAttempt == KAFKA_CONNECT_ATTEMPT) {
    +            break;
    +          }
    +        } else {
    +          kafkaAttempt = 0;
    +        }
    +
    +        boolean crossedBoundary = false;
    +
    +        for (ConsumerRecord consumerRecord : consumerRecords) {
    +
    +          if ( !doesKeyBelongsThisInstance(operatorId, (String)consumerRecord.key()) ) {
    +            continue;
    +          }
    +
    +          recoveredTuples.add((T)consumerRecord.value());
    +
    +          if ( consumerRecord.offset() >= currentOffset ) {
    +            crossedBoundary = true;
    +            break;
    +          }
    +        }
    +
    +        if ( crossedBoundary ) {
    +          break;
    +        }
    +      }
    +    }
    +
    +    consumer.close();
    +  }
    +
    +  private Map<Integer,Long> getCurrentOffsets()
    +  {
    +    Map<Integer, Long> currentOffsets = null;
    +
    +    try {
    +      currentOffsets = getPartitionsAndOffsets();
    +    } catch (ExecutionException e) {
    +      e.printStackTrace();
    +    } catch (InterruptedException e) {
    +      e.printStackTrace();
    +    }
    +
    +    return currentOffsets;
    +  }
    +
    +  private Map<Integer,Long> getStoredOffsets()
    +  {
    +    Map<Integer,Long> storedOffsets = null;
    +    try {
    +      storedOffsets = (Map<Integer,Long>)this.windowDataManager.load(operatorId, windowId);
    +    } catch (IOException e) {
    +      e.printStackTrace();
    +    }
    +
    +    return storedOffsets;
    +  }
    +
    +  private KafkaConsumer KafkaConsumerInit()
    +  {
    +    Properties props = new Properties();
    +    props.put("bootstrap.servers", getConfigProperties().get("bootstrap.servers"));
    --- End diff --
    
    Can you use Java Constants instead of hardcoding property strings?
    You can find the public static string constants in org.apache.kafka.clients.producer.ProducerConfig


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