[GitHub] [flink] tillrohrmann commented on a change in pull request #14425: [FLINK-19773][runtime] Implement ExponentialDelayStrategy

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tillrohrmann commented on a change in pull request #14425:
URL: https://github.com/apache/flink/pull/14425#discussion_r548010140



##########
File path: flink-core/src/main/java/org/apache/flink/api/common/restartstrategy/RestartStrategies.java
##########
@@ -85,6 +85,30 @@ public static FailureRateRestartStrategyConfiguration failureRateRestart(
 		return new FailureRateRestartStrategyConfiguration(failureRate, failureInterval, delayInterval);
 	}
 
+	/**
+	 * Generates a ExponentialDelayRestartStrategyConfiguration.
+	 *
+	 * @param initialBackoff Starting duration between restarts
+	 * @param maxBackoff The highest possible duration between restarts
+	 * @param backoffMultiplier Delay multiplier how many times is the delay longer than before
+	 * @param resetBackoffThreshold How long the job must run smoothly to reset the time interval
+	 * @param jitterFactor How much the delay may differ (in percentage)
+	 */
+	public static ExponentialDelayRestartStrategyConfiguration exponentialDelayRestart(
+		Time initialBackoff,
+		Time maxBackoff,
+		double backoffMultiplier,
+		Time resetBackoffThreshold,
+		double jitterFactor
+	) {

Review comment:
       nit: using the style of this file, the closing parenthesis is usually put in the same line as the last parameter.

##########
File path: flink-runtime/src/main/java/org/apache/flink/runtime/executiongraph/failover/flip1/ExponentialDelayRestartBackoffTimeStrategy.java
##########
@@ -0,0 +1,220 @@
+/*
+ * 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.executiongraph.failover.flip1;
+
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.configuration.RestartStrategyOptions;
+import org.apache.flink.util.clock.Clock;
+import org.apache.flink.util.clock.SystemClock;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+import static org.apache.flink.util.Preconditions.checkArgument;
+import static org.apache.flink.util.Preconditions.checkNotNull;
+
+/**
+ * Restart strategy which tries to restart indefinitely number of times with a exponential backoff time in between.

Review comment:
       ```suggestion
    * Restart strategy which tries to restart indefinitely number of times with an exponential backoff time in between.
   ```

##########
File path: flink-runtime/src/test/java/org/apache/flink/runtime/executiongraph/failover/flip1/ExponentialDelayRestartBackoffTimeStrategyTest.java
##########
@@ -0,0 +1,256 @@
+/*
+ * 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.executiongraph.failover.flip1;
+
+import org.apache.flink.util.TestLogger;
+import org.apache.flink.util.clock.ManualClock;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.Callable;
+import java.util.concurrent.TimeUnit;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.lessThanOrEqualTo;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Unit tests for {@link ExponentialDelayRestartBackoffTimeStrategy}.
+ */
+public class ExponentialDelayRestartBackoffTimeStrategyTest extends TestLogger {
+
+	private final Exception failure = new Exception();
+
+	@Test
+	public void testAlwaysRestart() throws Exception {
+		final ExponentialDelayRestartBackoffTimeStrategy restartStrategy =
+			new ExponentialDelayRestartBackoffTimeStrategy(
+				new ManualClock(),
+				1L,
+				3L,
+				2.0,
+				4L,
+				0.25);
+
+		for (int i = 0; i < 13; i++) {
+			assertTrue(restartStrategy.canRestart());
+			restartStrategy.notifyFailure(failure);
+		}
+	}
+
+	@Test
+	public void testInitialBackoff() throws Exception {
+		long initialBackoffMS = 42L;
+
+		final ExponentialDelayRestartBackoffTimeStrategy restartStrategy =
+			new ExponentialDelayRestartBackoffTimeStrategy(
+				new ManualClock(),
+				initialBackoffMS,
+				45L,
+				2.0,
+				8L,
+				0);
+
+		assertThat(restartStrategy.getBackoffTime(), is(initialBackoffMS));
+	}
+
+	@Test
+	public void testMaxBackoff() throws Exception {
+		final long maxBackoffMS = 6L;
+
+		final ExponentialDelayRestartBackoffTimeStrategy restartStrategy =
+			new ExponentialDelayRestartBackoffTimeStrategy(
+				new ManualClock(),
+				1L,
+				maxBackoffMS,
+				2.0,
+				8L,
+				0.25);
+
+		for (int i = 0; i < 10; i++) {
+			restartStrategy.notifyFailure(failure);
+			assertThat(restartStrategy.getBackoffTime(), lessThanOrEqualTo(maxBackoffMS));
+		}
+	}
+
+	@Test
+	public void testResetBackoff() throws Exception {
+		final long initialBackoffMS = 1L;
+		final long resetBackoffThresholdMS = 8L;
+		final ManualClock clock = new ManualClock();
+
+		final ExponentialDelayRestartBackoffTimeStrategy restartStrategy =
+			new ExponentialDelayRestartBackoffTimeStrategy(clock,
+				initialBackoffMS, 5L, 2.0, resetBackoffThresholdMS, 0.25);
+
+		clock.advanceTime(resetBackoffThresholdMS + restartStrategy.getBackoffTime() - 1, TimeUnit.MILLISECONDS);
+		restartStrategy.notifyFailure(failure);
+		assertThat("Backoff should be increased", restartStrategy.getBackoffTime(), is(2L));
+
+		clock.advanceTime(resetBackoffThresholdMS + restartStrategy.getBackoffTime(), TimeUnit.MILLISECONDS);
+		restartStrategy.notifyFailure(failure);
+		assertThat(
+			"Backoff should be reset",
+			restartStrategy.getBackoffTime(),
+			is(initialBackoffMS));
+	}
+
+	@Test
+	public void testBackoffMultiplier() throws Exception {
+		long initialBackoffMS = 4L;
+		double jitterFactor = 0;
+		double backoffMultiplier = 2.3;
+		long maxBackoffMS = 300L;
+
+		final ExponentialDelayRestartBackoffTimeStrategy restartStrategy =
+			new ExponentialDelayRestartBackoffTimeStrategy(
+				new ManualClock(),
+				initialBackoffMS,
+				maxBackoffMS,
+				backoffMultiplier,
+				8L,
+				jitterFactor);
+
+		restartStrategy.notifyFailure(failure);
+		assertThat(restartStrategy.getBackoffTime(), is(9L)); // 4 * 2.3
+
+		restartStrategy.notifyFailure(failure);
+		assertThat(restartStrategy.getBackoffTime(), is(20L)); // 9 * 2.3
+	}
+
+	@Test
+	public void testJitter() throws Exception {
+		final long initialBackoffMS = 2L;
+		final long maxBackoffMS = 7L;
+
+		final ExponentialDelayRestartBackoffTimeStrategy restartStrategy =
+			new ExponentialDelayRestartBackoffTimeStrategy(
+				new ManualClock(),
+				initialBackoffMS,
+				maxBackoffMS,
+				2.0,
+				1L,
+				0.25);
+
+		restartStrategy.notifyFailure(failure);
+		assertCorrectRandomRange(restartStrategy::getBackoffTime, 3L, 4L, 5L);
+
+		restartStrategy.notifyFailure(failure);
+		assertCorrectRandomRange(restartStrategy::getBackoffTime, 6L, 7L);
+
+		restartStrategy.notifyFailure(failure);
+		assertCorrectRandomRange(restartStrategy::getBackoffTime, 6L, 7L);
+	}
+
+	@Test
+	public void testJitterNoHigherThanMax() throws Exception {
+		double jitterFactor = 1;
+
+		final ExponentialDelayRestartBackoffTimeStrategy restartStrategy =
+			new ExponentialDelayRestartBackoffTimeStrategy(
+				new ManualClock(),
+				1L,
+				9L,
+				2.0,
+				8L,
+				jitterFactor);
+
+		assertCorrectRandomRange(restartStrategy::getBackoffTime, 0L, 1L, 2L);
+
+		restartStrategy.notifyFailure(failure);
+		assertCorrectRandomRange(restartStrategy::getBackoffTime, 0L, 1L, 2L, 3L, 4L);
+
+		restartStrategy.notifyFailure(failure);
+		assertCorrectRandomRange(
+			restartStrategy::getBackoffTime,
+			0L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L);

Review comment:
       Shouldn't we set the max backoff time to something like `7` in order to test that we will respect it? At the moment it is set to `9` which means that we won't exceed the max backoff time after three failures if I am not mistaken.




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