[FLINK-12577] Flink uses Kryo serializer if given a SpecificRecord type

• Type: Bug
• Status: Open
• Priority: Not a Priority
• Resolution: Unresolved
• Affects Version/s: 1.7.2, 1.8.0, 1.9.0, 1.10.0
• Component/s: API / Type Serialization System
• Labels: auto-deprioritized-major auto-deprioritized-minor
• Assignee: Unassigned
• Reporter: Nico Kruber
• Created: 21/May/19 14:58
• Updated: 25/Nov/21 10:43

Description

If a data stream does not return a subclass of SpecificRecord, Flink will actually infer a GenericTypeInfo and use kryo instead.

Example:

StreamExecutionEnvironment env = ...
env.getConfig().disableGenericTypes();

DataStream<Measurement> sourceStream = env.addSource(...);
DataStream<SpecificRecord> test = sourceStream.map(value -> new AggregatedSensorStatistics());

public class AggregatedSensorStatistics extends org.apache.avro.specific.SpecificRecordBase implements org.apache.avro.specific.SpecificRecord {...}

This will lead to

Exception in thread "main" java.lang.UnsupportedOperationException: Generic types have been disabled in the ExecutionConfig and type org.apache.avro.specific.SpecificRecord is treated as a generic type.
	at org.apache.flink.api.java.typeutils.GenericTypeInfo.createSerializer(GenericTypeInfo.java:86)
	at org.apache.flink.streaming.api.graph.StreamGraph.addOperator(StreamGraph.java:208)
	at org.apache.flink.streaming.api.graph.StreamGraphGenerator.transformOneInputTransform(StreamGraphGenerator.java:541)
	at org.apache.flink.streaming.api.graph.StreamGraphGenerator.transform(StreamGraphGenerator.java:166)
	at org.apache.flink.streaming.api.graph.StreamGraphGenerator.generateInternal(StreamGraphGenerator.java:132)
	at org.apache.flink.streaming.api.graph.StreamGraphGenerator.generate(StreamGraphGenerator.java:124)
	at org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.getStreamGraph(StreamExecutionEnvironment.java:1537)
	at org.apache.flink.streaming.api.environment.LocalStreamEnvironment.execute(LocalStreamEnvironment.java:89)
	at org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.execute(StreamExecutionEnvironment.java:1510)
	at com.ververica.training.statemigration.StateMigrationJobBase.createAndExecuteJob(StateMigrationJobBase.java:68)
	at com.ververica.training.statemigration.avro.StateMigrationJob.main(StateMigrationJob.java:13)

You may want some flexibility in your types and thus not provide the exact one like AggregatedSensorStatistics in this example. I don't see any reason we should disallow that behaviour.

Reason for this is that TypeExtractor#privateGetForClass() is having this code which only sees classes as Avro if they extend from SpecificRecord:

if (hasSuperclass(clazz, AVRO_SPECIFIC_RECORD_BASE_CLASS)) {
	return AvroUtils.getAvroUtils().createAvroTypeInfo(clazz);
}