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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5048) Kafka Consumer (0.9/0.10) threading model leads problematic cancellation behavior
Date Fri, 11 Nov 2016 17:57:59 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15657656#comment-15657656

ASF GitHub Bot commented on FLINK-5048:

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

    --- Diff: flink-streaming-connectors/flink-connector-kafka-0.9/src/main/java/org/apache/flink/streaming/connectors/kafka/internal/KafkaConsumerThread.java
    @@ -0,0 +1,325 @@
    + * 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.flink.streaming.connectors.kafka.internal;
    +import org.apache.flink.metrics.MetricGroup;
    +import org.apache.flink.streaming.connectors.kafka.internals.KafkaTopicPartitionState;
    +import org.apache.flink.streaming.connectors.kafka.internals.metrics.KafkaMetricWrapper;
    +import org.apache.kafka.clients.consumer.ConsumerRecords;
    +import org.apache.kafka.clients.consumer.KafkaConsumer;
    +import org.apache.kafka.clients.consumer.OffsetAndMetadata;
    +import org.apache.kafka.clients.consumer.OffsetCommitCallback;
    +import org.apache.kafka.common.Metric;
    +import org.apache.kafka.common.MetricName;
    +import org.apache.kafka.common.TopicPartition;
    +import org.apache.kafka.common.errors.WakeupException;
    +import org.slf4j.Logger;
    +import java.util.ArrayList;
    +import java.util.List;
    +import java.util.Map;
    +import java.util.Properties;
    +import java.util.concurrent.atomic.AtomicReference;
    +import static org.apache.flink.util.Preconditions.checkNotNull;
    + * The thread the runs the {@link KafkaConsumer}, connecting to the brokers and polling
    + * The thread pushes the data into a {@link Handover} to be picked up by the fetcher
that will
    + * deserialize and emit the records.
    + * 
    + * <p><b>IMPORTANT:</b> This thread must not be interrupted when attempting
to shut it down.
    + * The Kafka consumer code was found to not always handle interrupts well, and to even
    + * deadlock in certain situations.
    + * 
    + * <p>Implementation Note: This code is written to be reusable in later versions
of the KafkaConsumer.
    + * Because Kafka is not maintaining binary compatibility, we use a "call bridge" as an
    + * to the KafkaConsumer calls that change signature.
    + */
    +public class KafkaConsumerThread extends Thread {
    +	/** Logger for this consumer */
    +	final Logger log;
    --- End diff --

> Kafka Consumer (0.9/0.10) threading model leads problematic cancellation behavior
> ---------------------------------------------------------------------------------
>                 Key: FLINK-5048
>                 URL: https://issues.apache.org/jira/browse/FLINK-5048
>             Project: Flink
>          Issue Type: Bug
>          Components: Kafka Connector
>    Affects Versions: 1.1.3
>            Reporter: Stephan Ewen
>            Assignee: Stephan Ewen
>             Fix For: 1.2.0
> The {{FLinkKafkaConsumer}} (0.9 / 0.10) spawns a separate thread that operates the KafkaConsumer.
That thread is shielded from interrupts, because the Kafka Consumer has not been handling
thread interrupts well.
> Since that thread is also the thread that emits records, it may block in the network
stack (backpressure) or in chained operators. The later case leads to situations where cancellations
get very slow unless that thread would be interrupted (which it cannot be).
> I propose to change the thread model as follows:
>   - A spawned consumer thread pull from the KafkaConsumer and pushes its pulled batch
of records into a blocking queue (size one)
>   - The main thread of the task will pull the record batches from the blocking queue
and emit the records.
> This allows actually for some additional I/O overlay while limiting the additional memory
consumption - only two batches are ever held, one being fetched and one being emitted.

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