Retries with jitter

App-vNext · Jul 28, 2023 · 1d7a807 · 1d7a807
1 parent 9a63e4e
commit 1d7a807
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Showing 8 changed files with 89 additions and 50 deletions.
diff --git a/src/Polly.Core/PublicAPI.Unshipped.txt b/src/Polly.Core/PublicAPI.Unshipped.txt
@@ -319,9 +319,8 @@ Polly.Retry.OnRetryArguments.RetryDelay.get -> System.TimeSpan
 Polly.Retry.OnRetryArguments.RetryDelay.init -> void
 Polly.Retry.RetryBackoffType
 Polly.Retry.RetryBackoffType.Constant = 0 -> Polly.Retry.RetryBackoffType
-Polly.Retry.RetryBackoffType.Exponential = 2 -> Polly.Retry.RetryBackoffType
-Polly.Retry.RetryBackoffType.ExponentialWithJitter = 3 -> Polly.Retry.RetryBackoffType
 Polly.Retry.RetryBackoffType.Linear = 1 -> Polly.Retry.RetryBackoffType
+Polly.Retry.RetryBackoffType.Exponential = 2 -> Polly.Retry.RetryBackoffType
 Polly.Retry.RetryDelayArguments
 Polly.Retry.RetryDelayArguments.Attempt.get -> int
 Polly.Retry.RetryDelayArguments.Attempt.init -> void
@@ -350,6 +349,8 @@ Polly.Retry.RetryStrategyOptions<TResult>.RetryDelayGenerator.set -> void
 Polly.Retry.RetryStrategyOptions<TResult>.RetryStrategyOptions() -> void
 Polly.Retry.RetryStrategyOptions<TResult>.ShouldHandle.get -> System.Func<Polly.OutcomeArguments<TResult, Polly.Retry.RetryPredicateArguments>, System.Threading.Tasks.ValueTask<bool>>!
 Polly.Retry.RetryStrategyOptions<TResult>.ShouldHandle.set -> void
+Polly.Retry.RetryStrategyOptions<TResult>.UseJitter.get -> bool
+Polly.Retry.RetryStrategyOptions<TResult>.UseJitter.set -> void
 Polly.RetryResilienceStrategyBuilderExtensions
 Polly.Telemetry.ExecutionAttemptArguments
 Polly.Telemetry.ExecutionAttemptArguments.Attempt.get -> int

diff --git a/src/Polly.Core/Retry/RetryBackoffType.cs b/src/Polly.Core/Retry/RetryBackoffType.cs
@@ -38,17 +38,4 @@ public enum RetryBackoffType
     /// 200ms, 400ms, 800ms.
     /// </example>
     Exponential,
-
-    /// <summary>
-    /// Exponential delay with randomization retry type,
-    /// making sure to mitigate any correlations.
-    /// </summary>
-    /// <example>
-    /// 850ms, 1455ms, 3060ms.
-    /// </example>
-    /// <remarks>
-    /// In transient failures handling scenarios, this is the
-    /// <see href=" https://github.com/Polly-Contrib/Polly.Contrib.WaitAndRetry#new-jitter-recommendation"> recommended retry type</see>.
-    /// </remarks>
-    ExponentialWithJitter,
 }
diff --git a/src/Polly.Core/Retry/RetryHelper.cs b/src/Polly.Core/Retry/RetryHelper.cs
@@ -2,17 +2,30 @@ namespace Polly.Retry;
 
 internal static class RetryHelper
 {
+    private const double JitterFactor = 0.5;
+
     private const double ExponentialFactor = 2.0;
 
     public static bool IsValidDelay(TimeSpan delay) => delay >= TimeSpan.Zero;
 
-    public static TimeSpan GetRetryDelay(RetryBackoffType type, int attempt, TimeSpan baseDelay, ref double state, Func<double> randomizer)
+    public static TimeSpan GetRetryDelay(RetryBackoffType type, bool jitter, int attempt, TimeSpan baseDelay, ref double state, Func<double> randomizer)
     {
         if (baseDelay == TimeSpan.Zero)
         {
             return baseDelay;
         }
 
+        if (jitter)
+        {
+            return type switch
+            {
+                RetryBackoffType.Constant => ApplyJitter(baseDelay, randomizer),
+                RetryBackoffType.Linear => ApplyJitter(TimeSpan.FromMilliseconds((attempt + 1) * baseDelay.TotalMilliseconds), randomizer),
+                RetryBackoffType.Exponential => DecorrelatedJitterBackoffV2(attempt, baseDelay, ref state, randomizer),
+                _ => throw new ArgumentOutOfRangeException(nameof(type), type, "The retry backoff type is not supported.")
+            };
+        }
+
         return type switch
         {
             RetryBackoffType.Constant => baseDelay,
@@ -23,7 +36,6 @@ public static TimeSpan GetRetryDelay(RetryBackoffType type, int attempt, TimeSpa
             RetryBackoffType.Linear => (attempt + 1) * baseDelay,
             RetryBackoffType.Exponential => Math.Pow(ExponentialFactor, attempt) * baseDelay,
 #endif
-            RetryBackoffType.ExponentialWithJitter => DecorrelatedJitterBackoffV2(attempt, baseDelay, ref state, randomizer),
             _ => throw new ArgumentOutOfRangeException(nameof(type), type, "The retry backoff type is not supported.")
         };
     }
@@ -72,4 +84,7 @@ private static TimeSpan DecorrelatedJitterBackoffV2(int attempt, TimeSpan baseDe
 
         return TimeSpan.FromTicks((long)Math.Min(formulaIntrinsicValue * RpScalingFactor * targetTicksFirstDelay, maxTimeSpanDouble));
     }
+
+    private static TimeSpan ApplyJitter(TimeSpan delay, Func<double> randomizer)
+        => TimeSpan.FromMilliseconds(delay.TotalMilliseconds + ((delay.TotalMilliseconds * JitterFactor) * randomizer()));
 }
diff --git a/src/Polly.Core/Retry/RetryResilienceStrategy.cs b/src/Polly.Core/Retry/RetryResilienceStrategy.cs
@@ -23,6 +23,7 @@ public RetryResilienceStrategy(
         RetryCount = options.RetryCount;
         OnRetry = options.OnRetry;
         DelayGenerator = options.RetryDelayGenerator;
+        UseJitter = options.UseJitter;
 
         _timeProvider = timeProvider;
         _telemetry = telemetry;
@@ -39,6 +40,8 @@ public RetryResilienceStrategy(
 
     public Func<OutcomeArguments<T, RetryDelayArguments>, ValueTask<TimeSpan>>? DelayGenerator { get; }
 
+    public bool UseJitter { get; }
+
     public Func<OutcomeArguments<T, OnRetryArguments>, ValueTask>? OnRetry { get; }
 
     protected override async ValueTask<Outcome<T>> ExecuteCallbackAsync<TState>(Func<ResilienceContext, TState, ValueTask<Outcome<T>>> callback, ResilienceContext context, TState state)
@@ -62,7 +65,7 @@ protected override async ValueTask<Outcome<T>> ExecuteCallbackAsync<TState>(Func
                 return outcome;
             }
 
-            var delay = RetryHelper.GetRetryDelay(BackoffType, attempt, BaseDelay, ref retryState, _randomizer);
+            var delay = RetryHelper.GetRetryDelay(BackoffType, UseJitter, attempt, BaseDelay, ref retryState, _randomizer);
             if (DelayGenerator is not null)
             {
                 var delayArgs = new OutcomeArguments<T, RetryDelayArguments>(context, outcome, new RetryDelayArguments(attempt, delay));

diff --git a/src/Polly.Core/Retry/RetryStrategyOptions.TResult.cs b/src/Polly.Core/Retry/RetryStrategyOptions.TResult.cs
@@ -34,6 +34,18 @@ public class RetryStrategyOptions<TResult> : ResilienceStrategyOptions
     /// </value>
     public RetryBackoffType BackoffType { get; set; } = RetryConstants.DefaultBackoffType;
 
+    /// <summary>
+    /// Gets or sets a value indicating whether the jitter should be used when calculating the backoff delay between retries.
+    /// </summary>
+    /// <remarks>
+    /// See <see href="https://github.com/Polly-Contrib/Polly.Contrib.WaitAndRetry#new-jitter-recommendation"/> for more details
+    /// on how jitter can improve the resilience when the retries are correlated.
+    /// </remarks>
+    /// <value>
+    /// The default value is <see langword="false"/>.
+    /// </value>
+    public bool UseJitter { get; set; }
+
 #pragma warning disable IL2026 // Addressed with DynamicDependency on ValidationHelper.Validate method
     /// <summary>
     /// Gets or sets the base delay between retries.
@@ -45,9 +57,6 @@ public class RetryStrategyOptions<TResult> : ResilienceStrategyOptions
     /// <see cref="RetryBackoffType.Exponential"/>: Represents the median delay to target before the first retry.
     /// </item>
     /// <item>
-    /// <see cref="RetryBackoffType.ExponentialWithJitter"/>: Represents the median delay to target before the first retry.
-    /// </item>
-    /// <item>
     /// <see cref="RetryBackoffType.Linear"/>: Represents the initial delay, the following delays increasing linearly with this value.
     /// </item>
     /// <item>

diff --git a/test/Polly.Core.Tests/Retry/RetryHelperTests.cs b/test/Polly.Core.Tests/Retry/RetryHelperTests.cs
@@ -6,7 +6,7 @@ namespace Polly.Core.Tests.Retry;
 
 public class RetryHelperTests
 {
-    private readonly Func<double> _randomizer = new RandomUtil(0).NextDouble;
+    private Func<double> _randomizer = new RandomUtil(0).NextDouble;
 
     [Fact]
     public void IsValidDelay_Ok()
@@ -18,58 +18,81 @@ public void IsValidDelay_Ok()
         RetryHelper.IsValidDelay(TimeSpan.FromMilliseconds(-1)).Should().BeFalse();
     }
 
-    [Fact]
-    public void UnsupportedRetryBackoffType_Throws()
+    [InlineData(true)]
+    [InlineData(false)]
+    [Theory]
+    public void UnsupportedRetryBackoffType_Throws(bool jitter)
     {
         RetryBackoffType type = (RetryBackoffType)99;
 
         Assert.Throws<ArgumentOutOfRangeException>(() =>
         {
             double state = 0;
-            return RetryHelper.GetRetryDelay(type, 0, TimeSpan.FromSeconds(1), ref state, _randomizer);
+            return RetryHelper.GetRetryDelay(type, jitter, 0, TimeSpan.FromSeconds(1), ref state, _randomizer);
         });
     }
 
-    [Fact]
-    public void Constant_Ok()
+    [InlineData(true)]
+    [InlineData(false)]
+    [Theory]
+    public void Constant_Ok(bool jitter)
     {
         double state = 0;
+        if (jitter)
+        {
+            _randomizer = () => 0.5;
+        }
+
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, jitter, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, jitter, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, jitter, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        var expected = !jitter ? TimeSpan.FromSeconds(1) : TimeSpan.FromSeconds(1.25);
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, jitter, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(expected);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, jitter, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(expected);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Constant, jitter, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(expected);
     }
 
-    [Fact]
-    public void Linear_Ok()
+    [InlineData(true)]
+    [InlineData(false)]
+    [Theory]
+    public void Linear_Ok(bool jitter)
     {
         double state = 0;
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+
+        if (jitter)
+        {
+            _randomizer = () => 0.5;
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(2));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Linear, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(3));
+            RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1.25));
+            RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(2.5));
+            RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(3.75));
+        }
+        else
+        {
+            RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
+            RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(2));
+            RetryHelper.GetRetryDelay(RetryBackoffType.Linear, jitter, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(3));
+        }
     }
 
     [Fact]
     public void Exponential_Ok()
     {
         double state = 0;
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, false, 0, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, false, 1, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, false, 2, TimeSpan.Zero, ref state, _randomizer).Should().Be(TimeSpan.Zero);
 
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(2));
-        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(4));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, false, 0, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(1));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, false, 1, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(2));
+        RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, false, 2, TimeSpan.FromSeconds(1), ref state, _randomizer).Should().Be(TimeSpan.FromSeconds(4));
     }
 
     [InlineData(1)]
@@ -113,7 +136,7 @@ private static IReadOnlyList<TimeSpan> GetExponentialWithJitterBackoff(bool cont
 
         for (int i = 0; i < retryCount; i++)
         {
-            result.Add(RetryHelper.GetRetryDelay(RetryBackoffType.ExponentialWithJitter, i, baseDelay, ref state, random));
+            result.Add(RetryHelper.GetRetryDelay(RetryBackoffType.Exponential, true, i, baseDelay, ref state, random));
         }
 
         return result;

diff --git a/test/Polly.Core.Tests/Retry/RetryResilienceStrategyBuilderExtensionsTests.cs b/test/Polly.Core.Tests/Retry/RetryResilienceStrategyBuilderExtensionsTests.cs
@@ -107,7 +107,7 @@ public void AddRetry_InvalidOptions_Throws()
     [Fact]
     public void GetAggregatedDelay_ShouldReturnTheSameValue()
     {
-        var options = new RetryStrategyOptions { BackoffType = RetryBackoffType.ExponentialWithJitter };
+        var options = new RetryStrategyOptions { BackoffType = RetryBackoffType.Exponential, UseJitter = true };
 
         var delay = GetAggregatedDelay(options);
         GetAggregatedDelay(options).Should().Be(delay);

diff --git a/test/Polly.Extensions.Tests/Issues/IssuesTests.StrategiesPerEndpoint_1365.cs b/test/Polly.Extensions.Tests/Issues/IssuesTests.StrategiesPerEndpoint_1365.cs
@@ -49,7 +49,8 @@ public void StrategiesPerEndpoint_1365()
             {
                 builder.AddRetry(new()
                 {
-                    BackoffType = RetryBackoffType.ExponentialWithJitter,
+                    BackoffType = RetryBackoffType.Exponential,
+                    UseJitter = true,
                     RetryCount = endpointOptions.Retries,
                     StrategyName = $"{context.StrategyKey.EndpointName}-Retry",
                 });