io.numaproj.numaflow.sessionreducer.model.SessionReducer Maven / Gradle / Ivy
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package io.numaproj.numaflow.sessionreducer.model;
/**
* SessionReducer exposes methods for performing session reduce operations.
*/
public abstract class SessionReducer {
/**
* processMessage is invoked for each session reduce input message.
* It reads the input data from the datum and performs session reduce operations for the given keys.
* An output stream is provided for sending back the result to the session reduce output stream.
*
* @param keys message keys
* @param datum current message to be processed
* @param outputStreamObserver observer of the reduce result, which is used to send back session reduce responses
*/
public abstract void processMessage(
String[] keys,
Datum datum,
OutputStreamObserver outputStreamObserver);
/**
* handleEndOfStream handles the closure of the session reduce input stream.
* This method is invoked when the input session reduce stream is closed.
* It provides the capability of constructing final responses based on the messages processed so far.
*
* @param keys message keys
* @param outputStreamObserver observer of the reduce result, which is used to send back reduce responses
*/
public abstract void handleEndOfStream(
String[] keys,
OutputStreamObserver outputStreamObserver);
/**
* accumulator transforms the current state of the session into a byte array representation.
* This method is invoked when the session is to be merged with another session.
*
* e.g. For a session reducer which tracks the number of events in a session by keeping a count integer,
* accumulator() can represent the state of it by returning the byte array representation of the integer.
*
* @return the accumulator for the session reducer.
*/
public abstract byte[] accumulator();
/**
* mergeAccumulator merges the current session with another session.
*
* e.g. For session reducers which track the number of events in a session by keeping a count integer,
* and use the byte array representation of the integer to form the accumulator,
* mergeAccumulator() can parse the input accumulator to the corresponding count integer and add it
* to the current session count to complete a session merge operation.
*
* @param accumulator the accumulator of the session to be merged in.
*/
public abstract void mergeAccumulator(byte[] accumulator);
}