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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 Wed, 16 Nov 2016 19:51:58 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15671424#comment-15671424

ASF GitHub Bot commented on FLINK-5048:

Github user StephanEwen closed the pull request at:


> 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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