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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 Mon, 14 Nov 2016 06:59:59 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15662981#comment-15662981

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-0.10/src/test/java/org/apache/flink/streaming/connectors/kafka/KafkaShortRetention010ITCase.java
    @@ -1,34 +0,0 @@
    - * 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;
    -import org.junit.Test;
    -public class KafkaShortRetention010ITCase extends KafkaShortRetentionTestBase {
    --- End diff --
    I think with this removal, we can also completely remove the `runFailOnAutoOffsetResetNone()`
from the `KafkaShortRetentionTestBase`.
    The 0.8 connector runs `runFailOnAutoOffsetResetNoneEager()` instead of `runFailOnAutoOffsetResetNone()`.
I think this is what we actually should also be doing for 0.9+ connectors, testing only the
eager version, because that's a Flink-specific behaviour (just pointing this out, we can add
this as a separate future task as this probably requires some some work on 0.9+).

> 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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