Log-adjusted backoff logic. (#1855)

The effect of the change is that initial attempts with small delay
are spread out in time more, which increases the overall time that
events are stored.

Author: vkryachko

transport/transport-runtime/src/main/java/com/google/android/datatransport/runtime/scheduling/jobscheduling/SchedulerConfig.java

@@ -65,6 +65,8 @@ public abstract static class Builder {
 
   private static final long ONE_SECOND = 1000;
 
+  private static final long BACKOFF_LOG_BASE = 10000;
+
   public static SchedulerConfig getDefault(Clock clock) {
     return SchedulerConfig.builder()
         .addConfig(
@@ -135,10 +137,20 @@ public long getScheduleDelay(Priority priority, long minTimestamp, int attemptNu
     long timeDiff = minTimestamp - getClock().getTime();
     ConfigValue config = getValues().get(priority);
 
-    long delay = Math.max(((long) Math.pow(2, attemptNumber - 1)) * config.getDelta(), timeDiff);
+    long delay = Math.max(adjustedExponentialBackoff(attemptNumber, config.getDelta()), timeDiff);
     return Math.min(delay, config.getMaxAllowedDelay());
   }
 
+  private long adjustedExponentialBackoff(int attemptNumber, long delta) {
+    int attemptCoefficient = attemptNumber - 1;
+    long deltaOr2 = delta > 1 ? delta : 2;
+
+    double logValue = Math.log(BACKOFF_LOG_BASE) / Math.log(deltaOr2 * attemptCoefficient);
+    double logRegularized = Math.max(1, logValue);
+
+    return (long) (Math.pow(3, attemptCoefficient) * delta * logRegularized);
+  }
+
   @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
   public JobInfo.Builder configureJob(
       JobInfo.Builder builder, Priority priority, long minimumTimestamp, int attemptNumber) {

transport/transport-runtime/src/test/java/com/google/android/datatransport/runtime/scheduling/jobscheduling/ScheduleDelayTest.java

@@ -0,0 +1,77 @@
+// Copyright 2020 Google LLC
+//
+// Licensed 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 com.google.android.datatransport.runtime.scheduling.jobscheduling;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.android.datatransport.Priority;
+import com.google.android.datatransport.runtime.time.Clock;
+import com.google.android.datatransport.runtime.time.TestClock;
+import edu.emory.mathcs.backport.java.util.Collections;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+
+@RunWith(RobolectricTestRunner.class)
+public class ScheduleDelayTest {
+  private final Clock CLOCK = new TestClock(0);
+  private static final int MAX_DELAY = 86400;
+
+  @Test
+  public void getScheduleDelay_withDelta1_shouldBackoffAsExpected() {
+    SchedulerConfig config = createConfig(1);
+    long[] expectedDelays = new long[] {1, 39, 59, 138, 358, 972, 2702, 7632, 21795, 62721, 86400};
+    for (int i = 0; i < expectedDelays.length; i++) {
+      assertThat(config.getScheduleDelay(Priority.DEFAULT, 0, i + 1)).isEqualTo(expectedDelays[i]);
+    }
+  }
+
+  @Test
+  public void getScheduleDelay_withDelta30_shouldBackoffAsExpected() {
+    SchedulerConfig config = createConfig(30);
+    long[] expectedDelays = new long[] {30, 243, 607, 1657, 4674, 13400, 38789, 86400};
+    for (int i = 0; i < expectedDelays.length; i++) {
+      assertThat(config.getScheduleDelay(Priority.DEFAULT, 0, i + 1)).isEqualTo(expectedDelays[i]);
+    }
+  }
+
+  @Test
+  public void getScheduleDelay_withDelta24Hours_shouldBackoffAsExpected() {
+    SchedulerConfig config = createConfig(MAX_DELAY);
+    long[] expectedDelays = new long[] {86400, 86400, 86400};
+    for (int i = 0; i < expectedDelays.length; i++) {
+      assertThat(config.getScheduleDelay(Priority.DEFAULT, 0, i + 1)).isEqualTo(expectedDelays[i]);
+    }
+  }
+
+  private SchedulerConfig createConfig(int delta) {
+    return SchedulerConfig.builder()
+        .setClock(CLOCK)
+        .addConfig(
+            Priority.DEFAULT,
+            SchedulerConfig.ConfigValue.builder()
+                .setDelta(delta)
+                .setMaxAllowedDelay(MAX_DELAY)
+                .setFlags(Collections.emptySet())
+                .build())
+        .addConfig(
+            Priority.VERY_LOW,
+            SchedulerConfig.ConfigValue.builder().setDelta(0).setMaxAllowedDelay(0).build())
+        .addConfig(
+            Priority.HIGHEST,
+            SchedulerConfig.ConfigValue.builder().setDelta(0).setMaxAllowedDelay(0).build())
+        .build();
+  }
+}

transport/transport-runtime/src/test/java/com/google/android/datatransport/runtime/scheduling/jobscheduling/SchedulerConfigTest.java

@@ -34,7 +34,7 @@
 public class SchedulerConfigTest {
 
   private static final int DELTA = 10;
-  private static final int MAX_DELAY = 100;
+  private static final int MAX_DELAY = 86400;
   private final Clock CLOCK = new TestClock(0);
 
   @Test
@@ -64,13 +64,13 @@ public void build_whenNotAllPrioritiesSet_shouldThrow() {
     assertThat(ex.getMessage()).contains("priorities");
   }
 
-  private SchedulerConfig createConfig(Set<SchedulerConfig.Flag> flags) {
+  private SchedulerConfig createConfig(Set<SchedulerConfig.Flag> flags, int delta) {
     return SchedulerConfig.builder()
         .setClock(CLOCK)
         .addConfig(
             Priority.DEFAULT,
             SchedulerConfig.ConfigValue.builder()
-                .setDelta(DELTA)
+                .setDelta(delta)
                 .setMaxAllowedDelay(MAX_DELAY)
                 .setFlags(flags)
                 .build())
@@ -85,44 +85,49 @@ private SchedulerConfig createConfig(Set<SchedulerConfig.Flag> flags) {
 
   @Test
   public void getScheduleDelay_whenNoMinTimestampAndFirstAttempt_shouldReturnExpectedValue() {
-    long delay = createConfig(Collections.emptySet()).getScheduleDelay(Priority.DEFAULT, 0, 1);
+    long delay =
+        createConfig(Collections.emptySet(), DELTA).getScheduleDelay(Priority.DEFAULT, 0, 1);
 
     assertThat(delay).isEqualTo(10);
   }
 
   @Test
   public void getScheduleDelay_whenNoMinTimestampAndSecondAttempt_shouldReturnExpectedValue() {
-    long delay = createConfig(Collections.emptySet()).getScheduleDelay(Priority.DEFAULT, 0, 2);
+    long delay =
+        createConfig(Collections.emptySet(), DELTA).getScheduleDelay(Priority.DEFAULT, 0, 2);
 
-    assertThat(delay).isEqualTo(20);
+    assertThat(delay).isEqualTo(120);
   }
 
   @Test
   public void getScheduleDelay_withMinTimestampAndFirstAttempt_shouldReturnExpectedValue() {
-    long delay = createConfig(Collections.emptySet()).getScheduleDelay(Priority.DEFAULT, 50, 1);
+    long delay =
+        createConfig(Collections.emptySet(), DELTA).getScheduleDelay(Priority.DEFAULT, 50, 1);
 
     assertThat(delay).isEqualTo(50);
   }
 
   @Test
   public void getScheduleDelay_withMinTimestampAndFourthAttempt_shouldReturnExpectedValue() {
-    long delay = createConfig(Collections.emptySet()).getScheduleDelay(Priority.DEFAULT, 50, 4);
+    long delay =
+        createConfig(Collections.emptySet(), DELTA).getScheduleDelay(Priority.DEFAULT, 50, 4);
 
-    assertThat(delay).isEqualTo(80);
+    assertThat(delay).isEqualTo(731);
   }
 
   @Test
   public void getScheduleDelay_withMinTimestampAndFifthAttempt_shouldReturnMaxDelay() {
-    long delay = createConfig(Collections.emptySet()).getScheduleDelay(Priority.DEFAULT, 50, 5);
+    long delay =
+        createConfig(Collections.emptySet(), DELTA).getScheduleDelay(Priority.DEFAULT, 50, 5);
 
-    assertThat(delay).isEqualTo(100);
+    assertThat(delay).isEqualTo(2022);
   }
 
   @Test
   public void configureJob_shouldSetCorrectDelay() {
     ComponentName serviceComponent =
         new ComponentName(RuntimeEnvironment.application, JobInfoSchedulerService.class);
-    SchedulerConfig config = createConfig(Collections.emptySet());
+    SchedulerConfig config = createConfig(Collections.emptySet(), DELTA);
 
     JobInfo job =
         config
@@ -137,7 +142,7 @@ public void configureJob_shouldSetCorrectDelay() {
   public void configureJob_withDefaults_shouldSetCorrectFlags() {
     ComponentName serviceComponent =
         new ComponentName(RuntimeEnvironment.application, JobInfoSchedulerService.class);
-    SchedulerConfig config = createConfig(Collections.emptySet());
+    SchedulerConfig config = createConfig(Collections.emptySet(), DELTA);
 
     JobInfo job =
         config
@@ -153,7 +158,8 @@ public void configureJob_withDefaults_shouldSetCorrectFlags() {
   public void configureJob_whenUnmetered_shouldSetCorrectFlags() {
     ComponentName serviceComponent =
         new ComponentName(RuntimeEnvironment.application, JobInfoSchedulerService.class);
-    SchedulerConfig config = createConfig(EnumSet.of(SchedulerConfig.Flag.NETWORK_UNMETERED));
+    SchedulerConfig config =
+        createConfig(EnumSet.of(SchedulerConfig.Flag.NETWORK_UNMETERED), DELTA);
 
     JobInfo job =
         config
@@ -169,7 +175,7 @@ public void configureJob_whenUnmetered_shouldSetCorrectFlags() {
   public void configureJob_whenIdle_shouldSetCorrectFlags() {
     ComponentName serviceComponent =
         new ComponentName(RuntimeEnvironment.application, JobInfoSchedulerService.class);
-    SchedulerConfig config = createConfig(EnumSet.of(SchedulerConfig.Flag.DEVICE_IDLE));
+    SchedulerConfig config = createConfig(EnumSet.of(SchedulerConfig.Flag.DEVICE_IDLE), DELTA);
 
     JobInfo job =
         config
@@ -185,7 +191,7 @@ public void configureJob_whenIdle_shouldSetCorrectFlags() {
   public void configureJob_whenCharging_shouldSetCorrectFlags() {
     ComponentName serviceComponent =
         new ComponentName(RuntimeEnvironment.application, JobInfoSchedulerService.class);
-    SchedulerConfig config = createConfig(EnumSet.of(SchedulerConfig.Flag.DEVICE_CHARGING));
+    SchedulerConfig config = createConfig(EnumSet.of(SchedulerConfig.Flag.DEVICE_CHARGING), DELTA);
 
     JobInfo job =
         config