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Posted to commits@flink.apache.org by uc...@apache.org on 2017/01/24 13:36:33 UTC

[2/2] flink git commit: [FLINK-5615] [queryable state] Execute QueryableStateITCase for all backends

[FLINK-5615] [queryable state] Execute QueryableStateITCase for all backends

[FLINK-5615][query] improve testQueryableStateWithTaskManagerFailure test duration

This is based on the following points:
* slow down QueryableStateITCase#TestKeyRangeSource for the rest of the
  program to make more progress (we do not need a full-speed source here!)
* reduce the checkpointing interval
* reduce the amount of progress before starting our own evaluation
* reduce the number of checkpoints to wait for before killing a TM
* reduce the thread waiting time when asking how many checkpoints exist

Note that by slowing down QueryableStateITCase#TestKeyRangeSource, the other
tests should only be affected positively, too, since they also did not really
need a full-speed source and thus have more CPU cycles for their own tasks.

[FLINK-5615][query] speed up some more tests in QueryableStateITCase

This is based on reducing the number of keys the source generates. We do not
really need 1024 different keys for the tests - go with 256 now.

[FLINK-5615][query] execute the QueryableStateITCase for all state back-ends

[FLINK-5615][query] nicer test case abstraction

This closes #3194.


Project: http://git-wip-us.apache.org/repos/asf/flink/repo
Commit: http://git-wip-us.apache.org/repos/asf/flink/commit/b351aa2d
Tree: http://git-wip-us.apache.org/repos/asf/flink/tree/b351aa2d
Diff: http://git-wip-us.apache.org/repos/asf/flink/diff/b351aa2d

Branch: refs/heads/master
Commit: b351aa2ddd56bf0c20706400383fa4317bcdb03e
Parents: 19ef82c
Author: Nico Kruber <ni...@data-artisans.com>
Authored: Mon Jan 23 15:17:46 2017 +0100
Committer: Ufuk Celebi <uc...@apache.org>
Committed: Tue Jan 24 14:36:26 2017 +0100

----------------------------------------------------------------------
 .../query/AbstractQueryableStateITCase.java     | 1292 +++++++++++++++++
 .../flink/test/query/QueryableStateITCase.java  | 1297 ------------------
 .../query/QueryableStateITCaseFsBackend.java    |   38 +
 .../QueryableStateITCaseMemoryBackend.java      |   34 +
 .../QueryableStateITCaseRocksDBBackend.java     |   38 +
 5 files changed, 1402 insertions(+), 1297 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/flink/blob/b351aa2d/flink-tests/src/test/java/org/apache/flink/test/query/AbstractQueryableStateITCase.java
----------------------------------------------------------------------
diff --git a/flink-tests/src/test/java/org/apache/flink/test/query/AbstractQueryableStateITCase.java b/flink-tests/src/test/java/org/apache/flink/test/query/AbstractQueryableStateITCase.java
new file mode 100644
index 0000000..5683c5e
--- /dev/null
+++ b/flink-tests/src/test/java/org/apache/flink/test/query/AbstractQueryableStateITCase.java
@@ -0,0 +1,1292 @@
+/*
+ * 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.test.query;
+
+import akka.actor.ActorRef;
+import akka.actor.ActorSystem;
+import akka.actor.PoisonPill;
+import akka.dispatch.Futures;
+import akka.dispatch.Mapper;
+import akka.dispatch.OnSuccess;
+import akka.dispatch.Recover;
+import akka.pattern.Patterns;
+import org.apache.flink.api.common.JobID;
+import org.apache.flink.api.common.functions.FoldFunction;
+import org.apache.flink.api.common.functions.ReduceFunction;
+import org.apache.flink.api.common.restartstrategy.RestartStrategies;
+import org.apache.flink.api.common.state.FoldingStateDescriptor;
+import org.apache.flink.api.common.state.ReducingStateDescriptor;
+import org.apache.flink.api.common.state.ValueStateDescriptor;
+import org.apache.flink.api.common.typeutils.base.StringSerializer;
+import org.apache.flink.api.java.functions.KeySelector;
+import org.apache.flink.api.java.tuple.Tuple2;
+import org.apache.flink.configuration.ConfigConstants;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.configuration.QueryableStateOptions;
+import org.apache.flink.runtime.akka.AkkaUtils;
+import org.apache.flink.runtime.executiongraph.ExecutionAttemptID;
+import org.apache.flink.runtime.executiongraph.ExecutionGraph;
+import org.apache.flink.runtime.jobgraph.JobGraph;
+import org.apache.flink.runtime.jobgraph.JobStatus;
+import org.apache.flink.runtime.messages.JobManagerMessages;
+import org.apache.flink.runtime.messages.JobManagerMessages.CancellationSuccess;
+import org.apache.flink.runtime.messages.JobManagerMessages.JobFound;
+import org.apache.flink.runtime.query.KvStateLocation;
+import org.apache.flink.runtime.query.KvStateMessage;
+import org.apache.flink.runtime.query.QueryableStateClient;
+import org.apache.flink.runtime.query.netty.UnknownKeyOrNamespace;
+import org.apache.flink.runtime.query.netty.message.KvStateRequestSerializer;
+import org.apache.flink.runtime.state.AbstractStateBackend;
+import org.apache.flink.runtime.state.CheckpointListener;
+import org.apache.flink.runtime.state.VoidNamespace;
+import org.apache.flink.runtime.state.VoidNamespaceSerializer;
+import org.apache.flink.runtime.testingUtils.TestingCluster;
+import org.apache.flink.runtime.testingUtils.TestingTaskManagerMessages;
+import org.apache.flink.runtime.testingUtils.TestingTaskManagerMessages.ResponseRunningTasks;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import org.apache.flink.streaming.api.datastream.QueryableStateStream;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.streaming.api.functions.source.RichParallelSourceFunction;
+import org.apache.flink.util.MathUtils;
+import org.apache.flink.util.Preconditions;
+import org.apache.flink.util.TestLogger;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import scala.concurrent.Await;
+import scala.concurrent.Future;
+import scala.concurrent.duration.Deadline;
+import scala.concurrent.duration.FiniteDuration;
+import scala.reflect.ClassTag$;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicLongArray;
+
+import static org.apache.flink.runtime.testingUtils.TestingJobManagerMessages.ExecutionGraphFound;
+import static org.apache.flink.runtime.testingUtils.TestingJobManagerMessages.JobStatusIs;
+import static org.apache.flink.runtime.testingUtils.TestingJobManagerMessages.NotifyWhenJobStatus;
+import static org.apache.flink.runtime.testingUtils.TestingJobManagerMessages.RequestExecutionGraph;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+/**
+ * Base class for queryable state integration tests with a configurable state backend.
+ */
+public abstract class AbstractQueryableStateITCase extends TestLogger {
+
+	private final static FiniteDuration TEST_TIMEOUT = new FiniteDuration(100, TimeUnit.SECONDS);
+	private final static FiniteDuration QUERY_RETRY_DELAY = new FiniteDuration(100, TimeUnit.MILLISECONDS);
+
+	private static ActorSystem TEST_ACTOR_SYSTEM;
+
+	private final static int NUM_TMS = 2;
+	private final static int NUM_SLOTS_PER_TM = 4;
+	private final static int NUM_SLOTS = NUM_TMS * NUM_SLOTS_PER_TM;
+
+	/**
+	 * State backend to use.
+	 */
+	protected AbstractStateBackend stateBackend;
+
+	/**
+	 * Shared between all the test. Make sure to have at least NUM_SLOTS
+	 * available after your test finishes, e.g. cancel the job you submitted.
+	 */
+	private static TestingCluster cluster;
+
+	@BeforeClass
+	public static void setup() {
+		try {
+			Configuration config = new Configuration();
+			config.setInteger(ConfigConstants.TASK_MANAGER_MEMORY_SIZE_KEY, 4);
+			config.setInteger(ConfigConstants.LOCAL_NUMBER_TASK_MANAGER, NUM_TMS);
+			config.setInteger(ConfigConstants.TASK_MANAGER_NUM_TASK_SLOTS, NUM_SLOTS_PER_TM);
+			config.setInteger(QueryableStateOptions.CLIENT_NETWORK_THREADS, 1);
+			config.setBoolean(QueryableStateOptions.SERVER_ENABLE, true);
+			config.setInteger(QueryableStateOptions.SERVER_NETWORK_THREADS, 1);
+
+			cluster = new TestingCluster(config, false);
+			cluster.start(true);
+
+			TEST_ACTOR_SYSTEM = AkkaUtils.createDefaultActorSystem();
+		} catch (Exception e) {
+			e.printStackTrace();
+			fail(e.getMessage());
+		}
+	}
+
+	@AfterClass
+	public static void tearDown() {
+		try {
+			cluster.shutdown();
+		} catch (Exception e) {
+			e.printStackTrace();
+			fail(e.getMessage());
+		}
+
+		if (TEST_ACTOR_SYSTEM != null) {
+			TEST_ACTOR_SYSTEM.shutdown();
+		}
+	}
+
+	@Before
+	public void setUp() throws Exception {
+		// NOTE: do not use a shared instance for all tests as the tests may brake
+		this.stateBackend = createStateBackend();
+	}
+
+	/**
+	 * Creates a state backend instance which is used in the {@link #setUp()} method before each
+	 * test case.
+	 *
+	 * @return a state backend instance for each unit test
+	 */
+	protected abstract AbstractStateBackend createStateBackend() throws Exception;
+
+	/**
+	 * Runs a simple topology producing random (key, 1) pairs at the sources (where
+	 * number of keys is in fixed in range 0...numKeys). The records are keyed and
+	 * a reducing queryable state instance is created, which sums up the records.
+	 *
+	 * After submitting the job in detached mode, the QueryableStateCLient is used
+	 * to query the counts of each key in rounds until all keys have non-zero counts.
+	 */
+	@Test
+	@SuppressWarnings("unchecked")
+	public void testQueryableState() throws Exception {
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+		final int numKeys = 256;
+
+		final QueryableStateClient client = new QueryableStateClient(cluster.configuration());
+
+		JobID jobId = null;
+
+		try {
+			//
+			// Test program
+			//
+			StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+
+			DataStream<Tuple2<Integer, Long>> source = env
+					.addSource(new TestKeyRangeSource(numKeys));
+
+			// Reducing state
+			ReducingStateDescriptor<Tuple2<Integer, Long>> reducingState = new ReducingStateDescriptor<>(
+					"any-name",
+					new SumReduce(),
+					source.getType());
+
+			final String queryName = "hakuna-matata";
+
+			final QueryableStateStream<Integer, Tuple2<Integer, Long>> queryableState =
+					source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+							return value.f0;
+						}
+					}).asQueryableState(queryName, reducingState);
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			cluster.submitJobDetached(jobGraph);
+
+			//
+			// Start querying
+			//
+			jobId = jobGraph.getJobID();
+
+			final AtomicLongArray counts = new AtomicLongArray(numKeys);
+
+			boolean allNonZero = false;
+			while (!allNonZero && deadline.hasTimeLeft()) {
+				allNonZero = true;
+
+				final List<Future<byte[]>> futures = new ArrayList<>(numKeys);
+
+				for (int i = 0; i < numKeys; i++) {
+					final int key = i;
+
+					if (counts.get(key) > 0) {
+						// Skip this one
+						continue;
+					} else {
+						allNonZero = false;
+					}
+
+					final byte[] serializedKey = KvStateRequestSerializer.serializeKeyAndNamespace(
+							key,
+							queryableState.getKeySerializer(),
+							VoidNamespace.INSTANCE,
+							VoidNamespaceSerializer.INSTANCE);
+
+					Future<byte[]> serializedResult = getKvStateWithRetries(
+							client,
+							jobId,
+							queryName,
+							key,
+							serializedKey,
+							QUERY_RETRY_DELAY,
+							false);
+
+					serializedResult.onSuccess(new OnSuccess<byte[]>() {
+						@Override
+						public void onSuccess(byte[] result) throws Throwable {
+							Tuple2<Integer, Long> value = KvStateRequestSerializer.deserializeValue(
+									result,
+									queryableState.getValueSerializer());
+
+							counts.set(key, value.f1);
+
+							assertEquals("Key mismatch", key, value.f0.intValue());
+						}
+					}, TEST_ACTOR_SYSTEM.dispatcher());
+
+					futures.add(serializedResult);
+				}
+
+				Future<Iterable<byte[]>> futureSequence = Futures.sequence(
+						futures,
+						TEST_ACTOR_SYSTEM.dispatcher());
+
+				Await.ready(futureSequence, deadline.timeLeft());
+			}
+
+			assertTrue("Not all keys are non-zero", allNonZero);
+
+			// All should be non-zero
+			for (int i = 0; i < numKeys; i++) {
+				long count = counts.get(i);
+				assertTrue("Count at position " + i + " is " + count, count > 0);
+			}
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+						.getLeaderGateway(deadline.timeLeft())
+						.ask(new JobManagerMessages.CancelJob(jobId), deadline.timeLeft())
+						.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+
+			client.shutDown();
+		}
+	}
+
+	/**
+	 * Queries a random key and waits for some checkpoints to complete. After
+	 * that the task manager where this key was held is killed. Then query the
+	 * key again and check for the expected Exception. Finally, add another
+	 * task manager and re-query the key (expecting a count >= the previous
+	 * one).
+	 */
+	@Test
+	public void testQueryableStateWithTaskManagerFailure() throws Exception {
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+		final int numKeys = 256;
+
+		final QueryableStateClient client = new QueryableStateClient(cluster.configuration());
+
+		JobID jobId = null;
+
+		try {
+			//
+			// Test program
+			//
+			StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+			env.getCheckpointConfig().setCheckpointInterval(500);
+
+			DataStream<Tuple2<Integer, Long>> source = env
+					.addSource(new TestKeyRangeSource(numKeys));
+
+			// Reducing state
+			ReducingStateDescriptor<Tuple2<Integer, Long>> reducingState = new ReducingStateDescriptor<>(
+					"any-name",
+					new SumReduce(),
+					source.getType());
+
+			final String queryName = "hakuna-matata";
+
+			final QueryableStateStream<Integer, Tuple2<Integer, Long>> queryableState =
+					source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+							return value.f0;
+						}
+					}).asQueryableState(queryName, reducingState);
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			cluster.submitJobDetached(jobGraph);
+
+			//
+			// Start querying
+			//
+			jobId = jobGraph.getJobID();
+
+			final int key = ThreadLocalRandom.current().nextInt(numKeys);
+
+			// Query a random key
+			final byte[] serializedKey = KvStateRequestSerializer.serializeKeyAndNamespace(
+					key,
+					queryableState.getKeySerializer(),
+					VoidNamespace.INSTANCE,
+					VoidNamespaceSerializer.INSTANCE);
+
+			long countForKey = 0;
+
+			boolean success = false;
+			while (!success && deadline.hasTimeLeft()) {
+				Future<byte[]> serializedResultFuture = getKvStateWithRetries(
+						client,
+						jobId,
+						queryName,
+						key,
+						serializedKey,
+						QUERY_RETRY_DELAY,
+						false);
+
+				byte[] serializedResult = Await.result(serializedResultFuture, deadline.timeLeft());
+
+				Tuple2<Integer, Long> result = KvStateRequestSerializer.deserializeValue(
+						serializedResult,
+						queryableState.getValueSerializer());
+
+				countForKey = result.f1;
+
+				assertEquals("Key mismatch", key, result.f0.intValue());
+				success = countForKey > 3; // Wait for some progress
+			}
+
+			assertTrue("No progress for count", countForKey > 3);
+
+			long currentCheckpointId = TestKeyRangeSource.LATEST_CHECKPOINT_ID.get();
+			long waitUntilCheckpointId = currentCheckpointId + 2;
+
+			// Wait for some checkpoint after the query result
+			while (deadline.hasTimeLeft() &&
+					TestKeyRangeSource.LATEST_CHECKPOINT_ID.get() < waitUntilCheckpointId) {
+				Thread.sleep(100);
+			}
+
+			assertTrue("Did not complete enough checkpoints to continue",
+					TestKeyRangeSource.LATEST_CHECKPOINT_ID.get() >= waitUntilCheckpointId);
+
+			//
+			// Find out on which TaskManager the KvState is located and kill that TaskManager
+			//
+			// This is the subtask index
+			int keyGroupIndex = MathUtils.murmurHash(key) % NUM_SLOTS;
+
+			// Find out which task manager holds this key
+			Future<ExecutionGraph> egFuture = cluster.getLeaderGateway(deadline.timeLeft())
+					.ask(new RequestExecutionGraph(jobId), deadline.timeLeft())
+					.mapTo(ClassTag$.MODULE$.<ExecutionGraphFound>apply(ExecutionGraphFound.class))
+					.map(new Mapper<ExecutionGraphFound, ExecutionGraph>() {
+						@Override
+						public ExecutionGraph apply(ExecutionGraphFound found) {
+							return (ExecutionGraph) found.executionGraph();
+						}
+					}, TEST_ACTOR_SYSTEM.dispatcher());
+			ExecutionGraph eg = Await.result(egFuture, deadline.timeLeft());
+
+			Future<KvStateLocation> locationFuture = cluster
+					.getLeaderGateway(deadline.timeLeft())
+					.ask(new KvStateMessage.LookupKvStateLocation(jobId, queryName), deadline.timeLeft())
+					.mapTo(ClassTag$.MODULE$.<KvStateLocation>apply(KvStateLocation.class));
+
+			KvStateLocation location = Await.result(locationFuture, deadline.timeLeft());
+
+			ExecutionAttemptID executionId = eg.getJobVertex(location.getJobVertexId())
+					.getTaskVertices()[keyGroupIndex]
+					.getCurrentExecutionAttempt()
+					.getAttemptId();
+
+			List<ActorRef> taskManagers = cluster.getTaskManagersAsJava();
+			ActorRef taskManagerToKill = null;
+			for (ActorRef taskManager : taskManagers) {
+				Future<ResponseRunningTasks> runningFuture = Patterns.ask(
+						taskManager,
+						TestingTaskManagerMessages.getRequestRunningTasksMessage(),
+						deadline.timeLeft().toMillis())
+						.mapTo(ClassTag$.MODULE$.<ResponseRunningTasks>apply(ResponseRunningTasks.class));
+
+				ResponseRunningTasks running = Await.result(runningFuture, deadline.timeLeft());
+
+				if (running.asJava().containsKey(executionId)) {
+					taskManagerToKill = taskManager;
+					break;
+				}
+			}
+
+			assertNotNull("Did not find TaskManager holding the key", taskManagerToKill);
+
+			// Kill the task manager
+			taskManagerToKill.tell(PoisonPill.getInstance(), ActorRef.noSender());
+
+			success = false;
+			for (int i = 0; i < 10 && !success; i++) {
+				try {
+					// Wait for the expected error. We might have to retry if
+					// the query is very fast.
+					Await.result(client.getKvState(jobId, queryName, key, serializedKey), deadline.timeLeft());
+					Thread.sleep(500);
+				} catch (Throwable ignored) {
+					success = true;
+				}
+			}
+
+			assertTrue("Query did not fail", success);
+
+			// Now start another task manager
+			cluster.addTaskManager();
+
+			Future<byte[]> serializedResultFuture = getKvStateWithRetries(
+					client,
+					jobId,
+					queryName,
+					key,
+					serializedKey,
+					QUERY_RETRY_DELAY,
+					false);
+
+			byte[] serializedResult = Await.result(serializedResultFuture, deadline.timeLeft());
+
+			Tuple2<Integer, Long> result = KvStateRequestSerializer.deserializeValue(
+					serializedResult,
+					queryableState.getValueSerializer());
+
+			assertTrue("Count moved backwards", result.f1 >= countForKey);
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+						.getLeaderGateway(deadline.timeLeft())
+						.ask(new JobManagerMessages.CancelJob(jobId), deadline.timeLeft())
+						.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+
+			client.shutDown();
+		}
+	}
+
+	/**
+	 * Tests that duplicate query registrations fail the job at the JobManager.
+	 */
+	@Test
+	public void testDuplicateRegistrationFailsJob() throws Exception {
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+		final int numKeys = 256;
+
+		JobID jobId = null;
+
+		try {
+			//
+			// Test program
+			//
+			StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+
+			DataStream<Tuple2<Integer, Long>> source = env
+					.addSource(new TestKeyRangeSource(numKeys));
+
+			// Reducing state
+			ReducingStateDescriptor<Tuple2<Integer, Long>> reducingState = new ReducingStateDescriptor<>(
+					"any-name",
+					new SumReduce(),
+					source.getType());
+
+			final String queryName = "duplicate-me";
+
+			final QueryableStateStream<Integer, Tuple2<Integer, Long>> queryableState =
+					source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+							return value.f0;
+						}
+					}).asQueryableState(queryName, reducingState);
+
+			final QueryableStateStream<Integer, Tuple2<Integer, Long>> duplicate =
+					source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+							return value.f0;
+						}
+					}).asQueryableState(queryName);
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			jobId = jobGraph.getJobID();
+
+			Future<JobStatusIs> failedFuture = cluster
+					.getLeaderGateway(deadline.timeLeft())
+					.ask(new NotifyWhenJobStatus(jobId, JobStatus.FAILED), deadline.timeLeft())
+					.mapTo(ClassTag$.MODULE$.<JobStatusIs>apply(JobStatusIs.class));
+
+			cluster.submitJobDetached(jobGraph);
+
+			JobStatusIs jobStatus = Await.result(failedFuture, deadline.timeLeft());
+			assertEquals(JobStatus.FAILED, jobStatus.state());
+
+			// Get the job and check the cause
+			JobFound jobFound = Await.result(
+					cluster.getLeaderGateway(deadline.timeLeft())
+							.ask(new JobManagerMessages.RequestJob(jobId), deadline.timeLeft())
+							.mapTo(ClassTag$.MODULE$.<JobFound>apply(JobFound.class)),
+					deadline.timeLeft());
+
+			String failureCause = jobFound.executionGraph().getFailureCauseAsString();
+
+			assertTrue("Not instance of SuppressRestartsException", failureCause.startsWith("org.apache.flink.runtime.execution.SuppressRestartsException"));
+			int causedByIndex = failureCause.indexOf("Caused by: ");
+			String subFailureCause = failureCause.substring(causedByIndex + "Caused by: ".length());
+			assertTrue("Not caused by IllegalStateException", subFailureCause.startsWith("java.lang.IllegalStateException"));
+			assertTrue("Exception does not contain registration name", subFailureCause.contains(queryName));
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+						.getLeaderGateway(deadline.timeLeft())
+						.ask(new JobManagerMessages.CancelJob(jobId), deadline.timeLeft())
+						.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+		}
+	}
+
+	/**
+	 * Tests simple value state queryable state instance. Each source emits
+	 * (subtaskIndex, 0)..(subtaskIndex, numElements) tuples, which are then
+	 * queried. The tests succeeds after each subtask index is queried with
+	 * value numElements (the latest element updated the state).
+	 */
+	@Test
+	public void testValueState() throws Exception {
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+
+		final int numElements = 1024;
+
+		final QueryableStateClient client = new QueryableStateClient(cluster.configuration());
+
+		JobID jobId = null;
+		try {
+			StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+
+			DataStream<Tuple2<Integer, Long>> source = env
+					.addSource(new TestAscendingValueSource(numElements));
+
+			// Value state
+			ValueStateDescriptor<Tuple2<Integer, Long>> valueState = new ValueStateDescriptor<>(
+					"any",
+					source.getType());
+
+			QueryableStateStream<Integer, Tuple2<Integer, Long>> queryableState =
+					source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+							return value.f0;
+						}
+					}).asQueryableState("hakuna", valueState);
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			jobId = jobGraph.getJobID();
+
+			cluster.submitJobDetached(jobGraph);
+
+			// Now query
+			long expected = numElements;
+
+			executeValueQuery(deadline, client, jobId, queryableState,
+				expected);
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+						.getLeaderGateway(deadline.timeLeft())
+						.ask(new JobManagerMessages.CancelJob(jobId), deadline.timeLeft())
+						.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+
+			client.shutDown();
+		}
+	}
+
+	/**
+	 * Similar tests as {@link #testValueState()} but before submitting the
+	 * job, we already issue one request which fails.
+	 */
+	@Test
+	public void testQueryNonStartedJobState() throws Exception {
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+
+		final int numElements = 1024;
+
+		final QueryableStateClient client = new QueryableStateClient(cluster.configuration());
+
+		JobID jobId = null;
+		try {
+			StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+
+			DataStream<Tuple2<Integer, Long>> source = env
+				.addSource(new TestAscendingValueSource(numElements));
+
+			// Value state
+			ValueStateDescriptor<Tuple2<Integer, Long>> valueState = new ValueStateDescriptor<>(
+				"any",
+				source.getType(),
+				null);
+
+			QueryableStateStream<Integer, Tuple2<Integer, Long>> queryableState =
+				source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+					@Override
+					public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+						return value.f0;
+					}
+				}).asQueryableState("hakuna", valueState);
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			jobId = jobGraph.getJobID();
+
+			// Now query
+			long expected = numElements;
+
+			// query once
+			client.getKvState(jobId, queryableState.getQueryableStateName(), 0,
+				KvStateRequestSerializer.serializeKeyAndNamespace(
+					0,
+					queryableState.getKeySerializer(),
+					VoidNamespace.INSTANCE,
+					VoidNamespaceSerializer.INSTANCE));
+
+			cluster.submitJobDetached(jobGraph);
+
+			executeValueQuery(deadline, client, jobId, queryableState,
+				expected);
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+					.getLeaderGateway(deadline.timeLeft())
+					.ask(new JobManagerMessages.CancelJob(jobId), deadline.timeLeft())
+					.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+
+			client.shutDown();
+		}
+	}
+
+	/**
+	 * Retry a query for state for keys between 0 and {@link #NUM_SLOTS} until
+	 * <tt>expected</tt> equals the value of the result tuple's second field.
+	 */
+	private void executeValueQuery(final Deadline deadline,
+		final QueryableStateClient client, final JobID jobId,
+		final QueryableStateStream<Integer, Tuple2<Integer, Long>> queryableState,
+		final long expected) throws Exception {
+
+		for (int key = 0; key < NUM_SLOTS; key++) {
+			final byte[] serializedKey = KvStateRequestSerializer.serializeKeyAndNamespace(
+				key,
+				queryableState.getKeySerializer(),
+				VoidNamespace.INSTANCE,
+				VoidNamespaceSerializer.INSTANCE);
+
+			boolean success = false;
+			while (deadline.hasTimeLeft() && !success) {
+				Future<byte[]> future = getKvStateWithRetries(client,
+					jobId,
+					queryableState.getQueryableStateName(),
+					key,
+					serializedKey,
+					QUERY_RETRY_DELAY,
+					false);
+
+				byte[] serializedValue = Await.result(future, deadline.timeLeft());
+
+				Tuple2<Integer, Long> value = KvStateRequestSerializer.deserializeValue(
+					serializedValue,
+					queryableState.getValueSerializer());
+
+				assertEquals("Key mismatch", key, value.f0.intValue());
+				if (expected == value.f1) {
+					success = true;
+				} else {
+					// Retry
+					Thread.sleep(50);
+				}
+			}
+
+			assertTrue("Did not succeed query", success);
+		}
+	}
+
+	/**
+	 * Tests simple value state queryable state instance with a default value
+	 * set. Each source emits (subtaskIndex, 0)..(subtaskIndex, numElements)
+	 * tuples, the key is mapped to 1 but key 0 is queried which should throw
+	 * a {@link UnknownKeyOrNamespace} exception.
+	 *
+	 * @throws UnknownKeyOrNamespace thrown due querying a non-existent key
+	 */
+	@Test(expected = UnknownKeyOrNamespace.class)
+	public void testValueStateDefault() throws
+		Exception, UnknownKeyOrNamespace {
+
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+
+		final int numElements = 1024;
+
+		final QueryableStateClient client = new QueryableStateClient(cluster.configuration());
+
+		JobID jobId = null;
+		try {
+			StreamExecutionEnvironment env =
+				StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies
+				.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+
+			DataStream<Tuple2<Integer, Long>> source = env
+				.addSource(new TestAscendingValueSource(numElements));
+
+			// Value state
+			ValueStateDescriptor<Tuple2<Integer, Long>> valueState =
+				new ValueStateDescriptor<>(
+					"any",
+					source.getType(),
+					Tuple2.of(0, 1337l));
+
+			// only expose key "1"
+			QueryableStateStream<Integer, Tuple2<Integer, Long>>
+				queryableState =
+				source.keyBy(
+					new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(
+							Tuple2<Integer, Long> value) throws
+							Exception {
+							return 1;
+						}
+					}).asQueryableState("hakuna", valueState);
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			jobId = jobGraph.getJobID();
+
+			cluster.submitJobDetached(jobGraph);
+
+			// Now query
+			int key = 0;
+			final byte[] serializedKey =
+				KvStateRequestSerializer.serializeKeyAndNamespace(
+					key,
+					queryableState.getKeySerializer(),
+					VoidNamespace.INSTANCE,
+					VoidNamespaceSerializer.INSTANCE);
+
+			Future<byte[]> future = getKvStateWithRetries(client,
+				jobId,
+				queryableState.getQueryableStateName(),
+				key,
+				serializedKey,
+				QUERY_RETRY_DELAY,
+				true);
+
+			Await.result(future, deadline.timeLeft());
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+					.getLeaderGateway(deadline.timeLeft())
+					.ask(new JobManagerMessages.CancelJob(jobId),
+						deadline.timeLeft())
+					.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(
+						CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+
+			client.shutDown();
+		}
+	}
+
+	/**
+	 * Tests simple value state queryable state instance. Each source emits
+	 * (subtaskIndex, 0)..(subtaskIndex, numElements) tuples, which are then
+	 * queried. The tests succeeds after each subtask index is queried with
+	 * value numElements (the latest element updated the state).
+	 *
+	 * This is the same as the simple value state test, but uses the API shortcut.
+	 */
+	@Test
+	public void testValueStateShortcut() throws Exception {
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+
+		final int numElements = 1024;
+
+		final QueryableStateClient client = new QueryableStateClient(cluster.configuration());
+
+		JobID jobId = null;
+		try {
+			StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+
+			DataStream<Tuple2<Integer, Long>> source = env
+					.addSource(new TestAscendingValueSource(numElements));
+
+			// Value state shortcut
+			QueryableStateStream<Integer, Tuple2<Integer, Long>> queryableState =
+					source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+							return value.f0;
+						}
+					}).asQueryableState("matata");
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			jobId = jobGraph.getJobID();
+
+			cluster.submitJobDetached(jobGraph);
+
+			// Now query
+			long expected = numElements;
+
+			executeValueQuery(deadline, client, jobId, queryableState,
+				expected);
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+						.getLeaderGateway(deadline.timeLeft())
+						.ask(new JobManagerMessages.CancelJob(jobId), deadline.timeLeft())
+						.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+
+			client.shutDown();
+		}
+	}
+
+	/**
+	 * Tests simple folding state queryable state instance. Each source emits
+	 * (subtaskIndex, 0)..(subtaskIndex, numElements) tuples, which are then
+	 * queried. The folding state sums these up and maps them to Strings. The
+	 * test succeeds after each subtask index is queried with result n*(n+1)/2
+	 * (as a String).
+	 */
+	@Test
+	public void testFoldingState() throws Exception {
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+
+		final int numElements = 1024;
+
+		final QueryableStateClient client = new QueryableStateClient(cluster.configuration());
+
+		JobID jobId = null;
+		try {
+			StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+
+			DataStream<Tuple2<Integer, Long>> source = env
+					.addSource(new TestAscendingValueSource(numElements));
+
+			// Folding state
+			FoldingStateDescriptor<Tuple2<Integer, Long>, String> foldingState =
+					new FoldingStateDescriptor<>(
+							"any",
+							"0",
+							new SumFold(),
+							StringSerializer.INSTANCE);
+
+			QueryableStateStream<Integer, String> queryableState =
+					source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+							return value.f0;
+						}
+					}).asQueryableState("pumba", foldingState);
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			jobId = jobGraph.getJobID();
+
+			cluster.submitJobDetached(jobGraph);
+
+			// Now query
+			String expected = Integer.toString(numElements * (numElements + 1) / 2);
+
+			for (int key = 0; key < NUM_SLOTS; key++) {
+				final byte[] serializedKey = KvStateRequestSerializer.serializeKeyAndNamespace(
+						key,
+						queryableState.getKeySerializer(),
+						VoidNamespace.INSTANCE,
+						VoidNamespaceSerializer.INSTANCE);
+
+				boolean success = false;
+				while (deadline.hasTimeLeft() && !success) {
+					Future<byte[]> future = getKvStateWithRetries(client,
+							jobId,
+							queryableState.getQueryableStateName(),
+							key,
+							serializedKey,
+							QUERY_RETRY_DELAY,
+							false);
+
+					byte[] serializedValue = Await.result(future, deadline.timeLeft());
+
+					String value = KvStateRequestSerializer.deserializeValue(
+							serializedValue,
+							queryableState.getValueSerializer());
+
+					if (expected.equals(value)) {
+						success = true;
+					} else {
+						// Retry
+						Thread.sleep(50);
+					}
+				}
+
+				assertTrue("Did not succeed query", success);
+			}
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+						.getLeaderGateway(deadline.timeLeft())
+						.ask(new JobManagerMessages.CancelJob(jobId), deadline.timeLeft())
+						.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+
+			client.shutDown();
+		}
+	}
+
+	/**
+	 * Tests simple reducing state queryable state instance. Each source emits
+	 * (subtaskIndex, 0)..(subtaskIndex, numElements) tuples, which are then
+	 * queried. The reducing state instance sums these up. The test succeeds
+	 * after each subtask index is queried with result n*(n+1)/2.
+	 */
+	@Test
+	public void testReducingState() throws Exception {
+		// Config
+		final Deadline deadline = TEST_TIMEOUT.fromNow();
+
+		final int numElements = 1024;
+
+		final QueryableStateClient client = new QueryableStateClient(cluster.configuration());
+
+		JobID jobId = null;
+		try {
+			StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+			env.setStateBackend(stateBackend);
+			env.setParallelism(NUM_SLOTS);
+			// Very important, because cluster is shared between tests and we
+			// don't explicitly check that all slots are available before
+			// submitting.
+			env.setRestartStrategy(RestartStrategies.fixedDelayRestart(Integer.MAX_VALUE, 1000));
+
+			DataStream<Tuple2<Integer, Long>> source = env
+					.addSource(new TestAscendingValueSource(numElements));
+
+			// Reducing state
+			ReducingStateDescriptor<Tuple2<Integer, Long>> reducingState =
+					new ReducingStateDescriptor<>(
+							"any",
+							new SumReduce(),
+							source.getType());
+
+			QueryableStateStream<Integer, Tuple2<Integer, Long>> queryableState =
+					source.keyBy(new KeySelector<Tuple2<Integer, Long>, Integer>() {
+						@Override
+						public Integer getKey(Tuple2<Integer, Long> value) throws Exception {
+							return value.f0;
+						}
+					}).asQueryableState("jungle", reducingState);
+
+			// Submit the job graph
+			JobGraph jobGraph = env.getStreamGraph().getJobGraph();
+			jobId = jobGraph.getJobID();
+
+			cluster.submitJobDetached(jobGraph);
+
+			// Wait until job is running
+
+			// Now query
+			long expected = numElements * (numElements + 1) / 2;
+
+			executeValueQuery(deadline, client, jobId, queryableState,
+				expected);
+		} finally {
+			// Free cluster resources
+			if (jobId != null) {
+				Future<CancellationSuccess> cancellation = cluster
+						.getLeaderGateway(deadline.timeLeft())
+						.ask(new JobManagerMessages.CancelJob(jobId), deadline.timeLeft())
+						.mapTo(ClassTag$.MODULE$.<CancellationSuccess>apply(CancellationSuccess.class));
+
+				Await.ready(cancellation, deadline.timeLeft());
+			}
+
+			client.shutDown();
+		}
+	}
+
+	@SuppressWarnings("unchecked")
+	private static Future<byte[]> getKvStateWithRetries(
+			final QueryableStateClient client,
+			final JobID jobId,
+			final String queryName,
+			final int key,
+			final byte[] serializedKey,
+			final FiniteDuration retryDelay,
+			final boolean failForUknownKeyOrNamespace) {
+
+		return client.getKvState(jobId, queryName, key, serializedKey)
+				.recoverWith(new Recover<Future<byte[]>>() {
+					@Override
+					public Future<byte[]> recover(Throwable failure) throws Throwable {
+						if (failure instanceof AssertionError) {
+							return Futures.failed(failure);
+						} else if (failForUknownKeyOrNamespace &&
+								(failure instanceof UnknownKeyOrNamespace)) {
+							return Futures.failed(failure);
+						} else {
+							// At startup some failures are expected
+							// due to races. Make sure that they don't
+							// fail this test.
+							return Patterns.after(
+									retryDelay,
+									TEST_ACTOR_SYSTEM.scheduler(),
+									TEST_ACTOR_SYSTEM.dispatcher(),
+									new Callable<Future<byte[]>>() {
+										@Override
+										public Future<byte[]> call() throws Exception {
+											return getKvStateWithRetries(
+													client,
+													jobId,
+													queryName,
+													key,
+													serializedKey,
+													retryDelay,
+													failForUknownKeyOrNamespace);
+										}
+									});
+						}
+					}
+				}, TEST_ACTOR_SYSTEM.dispatcher());
+	}
+
+	/**
+	 * Test source producing (key, 0)..(key, maxValue) with key being the sub
+	 * task index.
+	 *
+	 * <p>After all tuples have been emitted, the source waits to be cancelled
+	 * and does not immediately finish.
+	 */
+	private static class TestAscendingValueSource extends RichParallelSourceFunction<Tuple2<Integer, Long>> {
+
+		private final long maxValue;
+		private volatile boolean isRunning = true;
+
+		public TestAscendingValueSource(long maxValue) {
+			Preconditions.checkArgument(maxValue >= 0);
+			this.maxValue = maxValue;
+		}
+
+		@Override
+		public void open(Configuration parameters) throws Exception {
+			super.open(parameters);
+		}
+
+		@Override
+		public void run(SourceContext<Tuple2<Integer, Long>> ctx) throws Exception {
+			// f0 => key
+			int key = getRuntimeContext().getIndexOfThisSubtask();
+			Tuple2<Integer, Long> record = new Tuple2<>(key, 0L);
+
+			long currentValue = 0;
+			while (isRunning && currentValue <= maxValue) {
+				synchronized (ctx.getCheckpointLock()) {
+					record.f1 = currentValue;
+					ctx.collect(record);
+				}
+
+				currentValue++;
+			}
+
+			while (isRunning) {
+				synchronized (this) {
+					this.wait();
+				}
+			}
+		}
+
+		@Override
+		public void cancel() {
+			isRunning = false;
+
+			synchronized (this) {
+				this.notifyAll();
+			}
+		}
+
+	}
+
+	/**
+	 * Test source producing (key, 1) tuples with random key in key range (numKeys).
+	 */
+	private static class TestKeyRangeSource extends RichParallelSourceFunction<Tuple2<Integer, Long>>
+			implements CheckpointListener {
+
+		private final static AtomicLong LATEST_CHECKPOINT_ID = new AtomicLong();
+		private final int numKeys;
+		private final ThreadLocalRandom random = ThreadLocalRandom.current();
+		private volatile boolean isRunning = true;
+
+		public TestKeyRangeSource(int numKeys) {
+			this.numKeys = numKeys;
+		}
+
+		@Override
+		public void open(Configuration parameters) throws Exception {
+			super.open(parameters);
+			if (getRuntimeContext().getIndexOfThisSubtask() == 0) {
+				LATEST_CHECKPOINT_ID.set(0);
+			}
+		}
+
+		@Override
+		public void run(SourceContext<Tuple2<Integer, Long>> ctx) throws Exception {
+			// f0 => key
+			Tuple2<Integer, Long> record = new Tuple2<>(0, 1L);
+
+			while (isRunning) {
+				synchronized (ctx.getCheckpointLock()) {
+					record.f0 = random.nextInt(numKeys);
+					ctx.collect(record);
+				}
+				// mild slow down
+				Thread.sleep(1);
+			}
+		}
+
+		@Override
+		public void cancel() {
+			isRunning = false;
+		}
+
+		@Override
+		public void notifyCheckpointComplete(long checkpointId) throws Exception {
+			if (getRuntimeContext().getIndexOfThisSubtask() == 0) {
+				LATEST_CHECKPOINT_ID.set(checkpointId);
+			}
+		}
+	}
+
+	private static class SumFold implements FoldFunction<Tuple2<Integer, Long>, String> {
+		@Override
+		public String fold(String accumulator, Tuple2<Integer, Long> value) throws Exception {
+			long acc = Long.valueOf(accumulator);
+			acc += value.f1;
+			return Long.toString(acc);
+		}
+	}
+
+	private static class SumReduce implements ReduceFunction<Tuple2<Integer, Long>> {
+		@Override
+		public Tuple2<Integer, Long> reduce(Tuple2<Integer, Long> value1, Tuple2<Integer, Long> value2) throws Exception {
+			value1.f1 += value2.f1;
+			return value1;
+		}
+	}
+
+}