Package org.apache.flink.table.runtime.operators.rank

Class UpdatableTopNFunction

  • All Implemented Interfaces:
    Serializable, Function, RichFunction, CheckpointedFunction
    public class UpdatableTopNFunction
extends AbstractTopNFunction
implements CheckpointedFunction
    A TopN function could handle updating stream. It is a fast version of RetractableTopNFunction which only hold top n data in state, and keep sorted map in heap. However, the function only works in some special scenarios: 1. sort field collation is ascending and its mono is decreasing, or sort field collation is descending and its mono is increasing 2. input data has unique keys and unique key must contain partition key 3. input stream could not contain DELETE record or UPDATE_BEFORE record
    See Also:
    Serialized Form

    • Method Detail

      • open

        public void open​(OpenContext openContext)
          throws Exception
        Description copied from interface: RichFunction
        Initialization method for the function. It is called before the actual working methods (like map or join) and thus suitable for one time setup work. For functions that are part of an iteration, this method will be invoked at the beginning of each iteration superstep.

        The openContext object passed to the function can be used for configuration and initialization. The openContext contains some necessary information that were configured on the function in the program composition. 

        
 public class MyFilter extends RichFilterFunction<String> {

     private String searchString;

     public void open(OpenContext openContext) {
         // initialize the value of searchString
     }

     public boolean filter(String value) {
         return value.equals(searchString);
     }
 }
        Specified by:
        open in interface RichFunction
        Overrides:
        open in class AbstractTopNFunction
        Parameters:
        openContext - The context containing information about the context in which the function is opened.
        Throws:
        Exception - Implementations may forward exceptions, which are caught by the runtime. When the runtime catches an exception, it aborts the task and lets the fail-over logic decide whether to retry the task execution.

      • initializeState

        public void initializeState​(FunctionInitializationContext context)
                     throws Exception
        Description copied from interface: CheckpointedFunction
        This method is called when the parallel function instance is created during distributed execution. Functions typically set up their state storing data structures in this method.
        Specified by:
        initializeState in interface CheckpointedFunction
        Parameters:
        context - the context for initializing the operator
        Throws:
        Exception - Thrown, if state could not be created ot restored.