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From Jean-Baptiste Onofré (JIRA) <j...@apache.org>
Subject [jira] [Commented] (BEAM-2669) Kryo serialization exception when DStreams containing non-Kryo-serializable data are cached
Date Mon, 24 Jul 2017 08:30:00 GMT

    [ https://issues.apache.org/jira/browse/BEAM-2669?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16098070#comment-16098070
] 

Jean-Baptiste Onofré commented on BEAM-2669:
--------------------------------------------

Thanks for the details !

> Kryo serialization exception when DStreams containing non-Kryo-serializable data are
cached
> -------------------------------------------------------------------------------------------
>
>                 Key: BEAM-2669
>                 URL: https://issues.apache.org/jira/browse/BEAM-2669
>             Project: Beam
>          Issue Type: Bug
>          Components: runner-spark
>    Affects Versions: 0.4.0, 0.5.0, 0.6.0, 2.0.0
>            Reporter: Aviem Zur
>            Assignee: Amit Sela
>
> Today, when we detect re-use of a dataset in Spark runner we eagerly cache it to avoid
calculating the same data multiple times.
> ([EvaluationContext.java|https://github.com/apache/beam/blob/v2.0.0/runners/spark/src/main/java/org/apache/beam/runners/spark/translation/EvaluationContext.java#L148])
> When the dataset is bounded, which in Spark is represented by an {{RDD}}, we call {{RDD#persist}}
and use storage level provided by the user via {{SparkPipelineOptions}}. ([BoundedDataset.java|https://github.com/apache/beam/blob/v2.0.0/runners/spark/src/main/java/org/apache/beam/runners/spark/translation/BoundedDataset.java#L103-L103])
> When the dataset is unbounded, which in Spark is represented by a {{DStream}} we call
{{DStream.cache()}} which defaults to persist the {{DStream}} using storage level {{MEMORY_ONLY_SER}}
([UnboundedDataset.java|https://github.com/apache/beam/blob/v2.0.0/runners/spark/src/main/java/org/apache/beam/runners/spark/translation/streaming/UnboundedDataset.java#L61])
>  ([DStream.scala|https://github.com/apache/spark/blob/v1.6.3/streaming/src/main/scala/org/apache/spark/streaming/dstream/DStream.scala#L169])
> Storage level {{MEMORY_ONLY_SER}} means Spark will serialize the data using its configured
serializer. Since we configure this to be Kryo in a hard coded fashion, this means the data
will be serialized using Kryo. ([SparkContextFactory.java|https://github.com/apache/beam/blob/v2.0.0/runners/spark/src/main/java/org/apache/beam/runners/spark/translation/SparkContextFactory.java#L99-L99])
> Due to this, if your {{DStream}} contains non-Kryo-serializable data you will encounter
Kryo serialization exceptions and your task will fail.
> Possible actions we should consider:
> # Remove the hard coded Spark serializer configuration, this should be taken from the
user's configuration of Spark, no real reason for us to interfere with this.
> # Use the user's configured storage level configuration from {{SparkPipelineOptions}}
when caching unbounded datasets ({{DStream}}s), same as we do for bounded datasets.
> # Make caching of re-used datasets configurable in {{SparkPipelineOptions}} (enable/disable).
Although overloading our configuration with more options is always something not to be taken
lightly.



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