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Anyway to read Cassandra as DataStream/DataSet in Flink?

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James Yu

Anyway to read Cassandra as DataStream/DataSet in Flink?

Hi,

I tried to treat Cassandra as the source of data in Flink with the information provided in the following links:
- https://stackoverflow.com/questions/43067681/read-data-from-cassandra-for-processing-in-flink
- https://www.javatips.net/api/flink-master/flink-examples/flink-examples-streaming/src/main/java/org/apache/flink/streaming/examples/async/AsyncIOExample.java

I got the AsyncWaitOperator exception when I run the task. According the the 1st link, this exception occurs due to network problem. However, the strange thing is that I am running Cassandra on my local VM with only 10 rows of data in the target table.

@Jicaar in 1st link also mentions that switching from RichAsyncFunction to RichMapFunction can avoid the AsyncWaitOperator exception, can someone with similar experience share how to do it in RichMapFunction?

AsyncWaitOperator exception trace -->

02:21:00.164 [AsyncIO-Emitter-Thread (Source: Custom Source -> async wait operator -> (Flat Map, Sink: Unnamed) (1/1))] INFO org.apache.flink.runtime.taskmanager.Task - Source: Custom Source -> async wait operator -> (Flat Map, Sink: Unnamed) (1/1) (2809cef511194e612b2cc65510f78c64) switched from RUNNING to FAILED.

java.lang.Exception: An async function call terminated with an exception. Failing the AsyncWaitOperator.

at org.apache.flink.streaming.api.operators.async.Emitter.output(Emitter.java:137) [flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.api.operators.async.Emitter.run(Emitter.java:85) [flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at java.lang.Thread.run(Thread.java:745) [na:1.8.0_60]

Caused by: org.apache.flink.streaming.runtime.tasks.ExceptionInChainedOperatorException: Could not forward element to next operator

at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:566) ~[flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:524) ~[flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:504) ~[flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.runtime.tasks.OperatorChain$BroadcastingOutputCollector.collect(OperatorChain.java:611) ~[flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.runtime.tasks.OperatorChain$BroadcastingOutputCollector.collect(OperatorChain.java:572) ~[flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:830) ~[flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:808) ~[flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.api.operators.TimestampedCollector.collect(TimestampedCollector.java:51) ~[flink-streaming-java_2.11-1.4.2.jar:1.4.2]

at org.apache.flink.streaming.api.operators.async.Emitter.output(Emitter.java:133) [flink-streaming-java_2.11-1.4.2.jar:1.4.2]

... 2 common frames omitted

Caused by: com.esotericsoftware.kryo.KryoException: java.util.ConcurrentModificationException

Serialization trace:

classes (sun.misc.Launcher$AppClassLoader)

classloader (java.security.ProtectionDomain)

context (java.security.AccessControlContext)

acc (org.apache.flink.runtime.execution.librarycache.FlinkUserCodeClassLoaders$ChildFirstClassLoader)

contextClassLoader (java.lang.Thread)

threads (java.lang.ThreadGroup)

groups (java.lang.ThreadGroup)

threadGroup (io.netty.util.concurrent.DefaultThreadFactory)

val$backingThreadFactory (com.google.common.util.concurrent.ThreadFactoryBuilder$1)

threadFactory (java.util.concurrent.ThreadPoolExecutor)

delegate (com.google.common.util.concurrent.MoreExecutors$ListeningDecorator)

blockingExecutor (com.datastax.driver.core.Cluster$Manager)

manager (com.datastax.driver.core.Host)

triedHosts (com.datastax.driver.core.ExecutionInfo)

info (com.datastax.driver.core.ArrayBackedResultSet$SinglePage)

at com.esotericsoftware.kryo.serializers.ObjectField.write(ObjectField.java:82) ~[kryo-2.24.0.jar:na]