[GitHub] flink issue #2051: [FLINK-3779] Add support for queryable state

[soniclavier]

Github user soniclavier commented on the issue:

    https://github.com/apache/flink/pull/2051
  
    Thanks Ufuk & Stephen for the reply,
    
    I tried the serializers suggested by you
    ```
    val typeHint = new TypeHint[Tuple2[Long,String]](){}
    val serializer = TypeInformation.of(typeHint).createSerializer(null)
    
    //also tried this
    val fieldSerializers = Array[TypeSerializer[_]](StringSerializer.INSTANCE, 
LongSerializer.INSTANCE)
    val serializer2 = new 
TupleSerializer(classOf[Tuple2[Long,String]].asInstanceOf[Class[_]].asInstanceOf[Class[Tuple2[String,
 Long]]], fieldSerializers)
    ```
    
    But both gives me compilation error at
    ```
    val serializedKey = KvStateRequestSerializer.serializeKeyAndNamespace(
          key,
          serializer2,
          VoidNamespace.INSTANCE,
          VoidNamespaceSerializer.INSTANCE)
    ```
    the compilation error is:
    ```
    Error:(43, 7) type mismatch;
    found   : 
org.apache.flink.api.common.typeutils.TypeSerializer[org.apache.flink.api.java.tuple.Tuple2[Long,String]]
     required: 
org.apache.flink.api.common.typeutils.TypeSerializer[java.io.Serializable]
    Note: org.apache.flink.api.java.tuple.Tuple2[Long,String] <: 
java.io.Serializable, but Java-defined class TypeSerializer is invariant in 
type T.
    You may wish to investigate a wildcard type such as `_ <: 
java.io.Serializable`. (SLS 3.2.10)
          serializer,
          ^
    ```
    
    I had seen this before when I tried to set the serializer from 
`queryableState.getKeySerializer` 
    
    Note : It works fine when I use the longer version of serializer that I 
created.


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