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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.query;

import org.apache.flink.api.common.JobID;
import org.apache.flink.runtime.jobmaster.KvStateLocationOracle;

import javax.annotation.Nullable;

/**
 * An interface for the Queryable State Client Proxy running on each Task Manager in the cluster.
 *
 * This proxy is where the Queryable State Client (potentially running outside your Flink
 * cluster) connects to, and his responsibility is to forward the client's requests to the rest
 * of the entities participating in fetching the requested state, and running within the cluster.
 *
 * 
These are:
 * 

 *      the {@link org.apache.flink.runtime.jobmaster.JobMaster Job Manager},
 *     which is responsible for sending the
 *     {@link org.apache.flink.runtime.taskexecutor.TaskExecutor Task Manager} storing
 *     the requested state, and 
 *      the Task Manager having the state itself.
 * 
 */
public interface KvStateClientProxy extends KvStateServer {

	/**
	 * Updates the active {@link org.apache.flink.runtime.jobmaster.JobMaster Job Manager}
	 * in case of change.
	 *
	 * This is useful in settings where high-availability is enabled and
	 * a failed Job Manager is replaced by a new one.
	 *
	 * 
IMPORTANT:  this method may be called by a different thread than
	 * the {@link #getKvStateLocationOracle(JobID)}.
	 *
	 * @param jobId identifying the job for which to update the key-value state location oracle
	 * @param kvStateLocationOracle the key-value state location oracle for the given {@link JobID},
	 *                                 or null if there is no oracle anymore
	 * */
	void updateKvStateLocationOracle(
		JobID jobId,
		@Nullable KvStateLocationOracle kvStateLocationOracle);

	/**
	 * Retrieves a future containing the currently leading key-value state location oracle.
	 *
	 * IMPORTANT:  this method may be called by a different thread than the
	 * {@link #updateKvStateLocationOracle(JobID, KvStateLocationOracle)}.
	 *
	 * @param jobId identifying the job for which to request the key-value state location oracle
	 * @return The key-value state location oracle for the given {@link JobID} or null if none.
	 */
	@Nullable KvStateLocationOracle getKvStateLocationOracle(JobID jobId);
}