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Date: Mon, 14 Nov 2016 06:59:59 +0000 (UTC)
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Subject: [jira] [Commented] (FLINK-5048) Kafka Consumer (0.9/0.10) threading
 model leads problematic cancellation behavior
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archived-at: Mon, 14 Nov 2016 07:00:01 -0000


    [ https://issues.apache.org/jira/browse/FLINK-5048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15662978#comment-15662978 ] 

ASF GitHub Bot commented on FLINK-5048:
---------------------------------------

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

    https://github.com/apache/flink/pull/2789#discussion_r87734223
  
    --- Diff: flink-streaming-connectors/flink-connector-kafka-0.10/src/main/java/org/apache/flink/streaming/connectors/kafka/internal/KafkaConsumerCallBridge010.java ---
    @@ -0,0 +1,40 @@
    +/*
    + * 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.kafka.clients.consumer.KafkaConsumer;
    +import org.apache.kafka.common.TopicPartition;
    +
    +import java.util.List;
    +
    +/**
    + * The ConsumerCallBridge simply calls the {@link KafkaConsumer#assign(java.util.Collection)} method.
    + * 
    + * This indirection is necessary, because Kafka broke binary compatibility between 0.9 and 0.10,
    + * changing {@code assign(List)} to {@code assign(Collection)}.
    + * 
    + * Because of that, we need to two versions whose compiled code goes against different method signatures.
    --- End diff --
    
    nit: we need "to" two versions <-- redundant "to".


> 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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