ClientRetryPolicy: Adds Cross Regional Retry Logic on 429/3092

Microsoft.Azure.Cosmos/src/ClientRetryPolicy.cs

@@ -35,6 +35,7 @@ internal sealed class ClientRetryPolicy : IDocumentClientRetryPolicy
         private int serviceUnavailableRetryCount;
         private bool isReadRequest;
         private bool canUseMultipleWriteLocations;
+        private bool isMultiMasterWriteRequest;
         private Uri locationEndpoint;
         private RetryContext retryContext;
         private DocumentServiceRequest documentServiceRequest;
@@ -57,6 +58,7 @@ public ClientRetryPolicy(
             this.sessionTokenRetryCount = 0;
             this.serviceUnavailableRetryCount = 0;
             this.canUseMultipleWriteLocations = false;
+            this.isMultiMasterWriteRequest = false;
             this.isPertitionLevelFailoverEnabled = isPertitionLevelFailoverEnabled;
         }
 
@@ -97,6 +99,23 @@ public async Task<ShouldRetryResult> ShouldRetryAsync(
 
             if (exception is DocumentClientException clientException)
             {
+                // Today, the only scenario where we would treat a throttling (429) exception as service unavailable is when we
+                // get 429 (TooManyRequests) with sub status code 3092 (System Resource Not Available). Note that this is applicable
+                // for write requests targeted to a multiple master account. In such case, the 429/3092 will be treated as 503. The
+                // reason to keep the code out of the throttling retry policy is that in the near future, the 3092 sub status code
+                // might not be a throttling scenario at all and the status code in that case would be different than 429.
+                if (this.ShouldMarkEndpointUnavailableOnSystemResourceUnavailableForWrite(
+                    clientException.StatusCode,
+                    clientException.GetSubStatus()))
+                {
+                    DefaultTrace.TraceError(
+                        "Operation will NOT be retried on local region. Treating SystemResourceUnavailable (429/3092) as ServiceUnavailable (503). Status code: {0}, sub status code: {1}.",
+                        StatusCodes.TooManyRequests, SubStatusCodes.SystemResourceUnavailable);
+
+                    return this.TryMarkEndpointUnavailableForPkRangeAndRetryOnServiceUnavailable(
+                        shouldMarkEndpointUnavailableForPkRange: true);
+                }
+
                 ShouldRetryResult shouldRetryResult = await this.ShouldRetryInternalAsync(
                     clientException?.StatusCode,
                     clientException?.GetSubStatus());
@@ -143,6 +162,23 @@ public async Task<ShouldRetryResult> ShouldRetryAsync(
                 return shouldRetryResult;
             }
 
+            // Today, the only scenario where we would treat a throttling (429) exception as service unavailable is when we
+            // get 429 (TooManyRequests) with sub status code 3092 (System Resource Not Available). Note that this is applicable
+            // for write requests targeted to a multiple master account. In such case, the 429/3092 will be treated as 503. The
+            // reason to keep the code out of the throttling retry policy is that in the near future, the 3092 sub status code
+            // might not be a throttling scenario at all and the status code in that case would be different than 429.
+            if (this.ShouldMarkEndpointUnavailableOnSystemResourceUnavailableForWrite(
+                cosmosResponseMessage.StatusCode,
+                cosmosResponseMessage?.Headers.SubStatusCode))
+            {
+                DefaultTrace.TraceError(
+                    "Operation will NOT be retried on local region. Treating SystemResourceUnavailable (429/3092) as ServiceUnavailable (503). Status code: {0}, sub status code: {1}.",
+                    StatusCodes.TooManyRequests, SubStatusCodes.SystemResourceUnavailable);
+
+                return this.TryMarkEndpointUnavailableForPkRangeAndRetryOnServiceUnavailable(
+                    shouldMarkEndpointUnavailableForPkRange: true);
+            }
+
             return await this.throttlingRetry.ShouldRetryAsync(cosmosResponseMessage, cancellationToken);
         }
 
@@ -156,6 +192,8 @@ public void OnBeforeSendRequest(DocumentServiceRequest request)
             this.isReadRequest = request.IsReadOnlyRequest;
             this.canUseMultipleWriteLocations = this.globalEndpointManager.CanUseMultipleWriteLocations(request);
             this.documentServiceRequest = request;
+            this.isMultiMasterWriteRequest = !this.isReadRequest
+                && (this.globalEndpointManager?.CanSupportMultipleWriteLocations(request) ?? false);
 
             // clear previous location-based routing directive
             request.RequestContext.ClearRouteToLocation();
@@ -274,16 +312,8 @@ private async Task<ShouldRetryResult> ShouldRetryInternalAsync(
             // Received 503 due to client connect timeout or Gateway
             if (statusCode == HttpStatusCode.ServiceUnavailable)
             {
-                DefaultTrace.TraceWarning("ClientRetryPolicy: ServiceUnavailable. Refresh cache and retry. Failed Location: {0}; ResourceAddress: {1}",
-                    this.documentServiceRequest?.RequestContext?.LocationEndpointToRoute?.ToString() ?? string.Empty,
-                    this.documentServiceRequest?.ResourceAddress ?? string.Empty);
-
-                // Mark the partition as unavailable.
-                // Let the ClientRetry logic decide if the request should be retried
-                this.partitionKeyRangeLocationCache.TryMarkEndpointUnavailableForPartitionKeyRange(
-                     this.documentServiceRequest);
-
-                return this.ShouldRetryOnServiceUnavailable();
+                return this.TryMarkEndpointUnavailableForPkRangeAndRetryOnServiceUnavailable(
+                    shouldMarkEndpointUnavailableForPkRange: true);
             }
 
             return null;
@@ -406,6 +436,33 @@ private ShouldRetryResult ShouldRetryOnSessionNotAvailable(DocumentServiceReques
             }
         }
 
+        /// <summary>
+        /// Attempts to mark the endpoint associated with the current partition key range as unavailable and determines if
+        /// a retry should be performed due to a ServiceUnavailable (503) response. This method is invoked when a 503
+        /// Service Unavailable response is received, indicating that the service might be temporarily unavailable.
+        /// It optionally marks the partition key range as unavailable, which will influence future routing decisions.
+        /// </summary>
+        /// <param name="shouldMarkEndpointUnavailableForPkRange">A boolean flag indicating whether the endpoint for the
+        /// current partition key range should be marked as unavailable.</param>
+        /// <returns>An instance of <see cref="ShouldRetryResult"/> indicating whether the operation should be retried.</returns>
+        private ShouldRetryResult TryMarkEndpointUnavailableForPkRangeAndRetryOnServiceUnavailable(
+            bool shouldMarkEndpointUnavailableForPkRange)
+        {
+            DefaultTrace.TraceWarning("ClientRetryPolicy: ServiceUnavailable. Refresh cache and retry. Failed Location: {0}; ResourceAddress: {1}",
+                this.documentServiceRequest?.RequestContext?.LocationEndpointToRoute?.ToString() ?? string.Empty,
+                this.documentServiceRequest?.ResourceAddress ?? string.Empty);
+
+            if (shouldMarkEndpointUnavailableForPkRange)
+            {
+                // Mark the partition as unavailable.
+                // Let the ClientRetry logic decide if the request should be retried
+                this.partitionKeyRangeLocationCache.TryMarkEndpointUnavailableForPartitionKeyRange(
+                     this.documentServiceRequest);
+            }
+
+            return this.ShouldRetryOnServiceUnavailable();
+        }
+
         /// <summary>
         /// For a ServiceUnavailable (503.0) we could be having a timeout from Direct/TCP locally or a request to Gateway request with a similar response due to an endpoint not yet available.
         /// We try and retry the request only if there are other regions available. The retry logic is applicable for single master write accounts as well.
@@ -449,6 +506,24 @@ private ShouldRetryResult ShouldRetryOnServiceUnavailable()
             return ShouldRetryResult.RetryAfter(TimeSpan.Zero);
         }
 
+        /// <summary>
+        /// Returns a boolean flag indicating if the endpoint should be marked as unavailable
+        /// due to a 429 response with a sub status code of 3092 (system resource unavailable).
+        /// This is applicable for write requests targeted for multi master accounts.
+        /// </summary>
+        /// <param name="statusCode">An instance of <see cref="HttpStatusCode"/> containing the status code.</param>
+        /// <param name="subStatusCode">An instance of <see cref="SubStatusCodes"/> containing the sub status code.</param>
+        /// <returns>A boolean flag indicating is the endpoint should be marked as unavailable.</returns>
+        private bool ShouldMarkEndpointUnavailableOnSystemResourceUnavailableForWrite(
+            HttpStatusCode? statusCode,
+            SubStatusCodes? subStatusCode)
+        {
+            return this.isMultiMasterWriteRequest
+                && statusCode.HasValue
+                && (int)statusCode.Value == (int)StatusCodes.TooManyRequests
+                && subStatusCode == SubStatusCodes.SystemResourceUnavailable;
+        }
+
         private sealed class RetryContext
         {
             public int RetryLocationIndex { get; set; }

Microsoft.Azure.Cosmos/src/Routing/GlobalEndpointManager.cs

@@ -534,6 +534,20 @@ public virtual async Task RefreshLocationAsync(bool forceRefresh = false)
 
             await this.RefreshDatabaseAccountInternalAsync(forceRefresh: forceRefresh);
         }
+
+        /// <summary>
+        /// Determines whether the current configuration and state of the service allow for supporting multiple write locations.
+        /// This method returns True is the AvailableWriteLocations in LocationCache is more than 1. Otherwise, it returns False.
+        /// </summary>
+        /// <param name="request">The document service request for which the write location support is being evaluated.</param>
+        /// <returns>A boolean flag indicating if the available write locations are more than one.</returns>
+        public bool CanSupportMultipleWriteLocations(DocumentServiceRequest request)
+        {
+            return this.locationCache.CanUseMultipleWriteLocations()
+                && this.locationCache.GetAvailableWriteLocations()?.Count > 1
+                && (request.ResourceType == ResourceType.Document ||
+                (request.ResourceType == ResourceType.StoredProcedure && request.OperationType == OperationType.Execute));
+        }
 
 #pragma warning disable VSTHRD100 // Avoid async void methods
         private async void StartLocationBackgroundRefreshLoop()

Microsoft.Azure.Cosmos/src/Routing/IGlobalEndpointManager.cs

@@ -36,5 +36,7 @@ internal interface IGlobalEndpointManager : IDisposable
         ReadOnlyDictionary<string, Uri> GetAvailableWriteEndpointsByLocation();
 
         ReadOnlyDictionary<string, Uri> GetAvailableReadEndpointsByLocation();
+
+        bool CanSupportMultipleWriteLocations(DocumentServiceRequest request);
     }
 }

Microsoft.Azure.Cosmos/src/Routing/LocationCache.cs

@@ -263,6 +263,11 @@ public ReadOnlyCollection<string> GetAvailableReadLocations()
         {
             return this.locationInfo.AvailableReadLocations;
         }
+
+        public ReadOnlyCollection<string> GetAvailableWriteLocations()
+        {
+            return this.locationInfo.AvailableWriteLocations;
+        }
 
         /// <summary>
         /// Resolves request to service endpoint. 
@@ -532,8 +537,8 @@ public bool CanUseMultipleWriteLocations(DocumentServiceRequest request)
             return this.CanUseMultipleWriteLocations() &&
                 (request.ResourceType == ResourceType.Document ||
                 (request.ResourceType == ResourceType.StoredProcedure && request.OperationType == Documents.OperationType.ExecuteJavaScript));
-        }
-
+        }
+
         private void ClearStaleEndpointUnavailabilityInfo()
         {
             if (this.locationUnavailablityInfoByEndpoint.Any())
@@ -768,7 +773,7 @@ private ReadOnlyDictionary<string, Uri> GetEndpointByLocation(IEnumerable<Accoun
             return new ReadOnlyDictionary<string, Uri>(endpointsByLocation);
         }
 
-        private bool CanUseMultipleWriteLocations()
+        internal bool CanUseMultipleWriteLocations()
         {
             return this.useMultipleWriteLocations && this.enableMultipleWriteLocations;
         }

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/ClientRetryPolicyTests.cs

@@ -86,6 +86,82 @@ public void MultimasterMetadataWriteRetryTest()
             retryPolicy.OnBeforeSendRequest(request);
             Assert.AreEqual(request.RequestContext.LocationEndpointToRoute, ClientRetryPolicyTests.Location1Endpoint);
         }
+
+        /// <summary>
+        /// Test to validate that when 429.3092 is thrown from the service, write requests on
+        /// a multi master account should be converted to 503 and retried to the next region.
+        /// </summary>
+        [TestMethod]
+        [DataRow(true, DisplayName = "Validate retry policy with multi master write account.")]
+        [DataRow(false, DisplayName = "Validate retry policy with single master write account.")]
+        public async Task ShouldRetryAsync_WhenRequestThrottledWithResourceNotAvailable_ShouldThrow503OnMultiMasterWriteAndRetryOnNextRegion(
+            bool isMultiMasterAccount)
+        {
+            // Arrange.
+            const bool enableEndpointDiscovery = true;
+            using GlobalEndpointManager endpointManager = this.Initialize(
+                useMultipleWriteLocations: isMultiMasterAccount,
+                enableEndpointDiscovery: enableEndpointDiscovery,
+                isPreferredLocationsListEmpty: false,
+                multimasterMetadataWriteRetryTest: true);
+
+            await endpointManager.RefreshLocationAsync();
+
+            ClientRetryPolicy retryPolicy = new (
+                endpointManager,
+                this.partitionKeyRangeLocationCache,
+                new RetryOptions(),
+                enableEndpointDiscovery,
+                false);
+
+            // Creates a sample write request.
+            DocumentServiceRequest request = this.CreateRequest(
+                isReadRequest: false,
+                isMasterResourceType: false);
+
+            // On first attempt should get (default/non hub) location.
+            retryPolicy.OnBeforeSendRequest(request);
+            Assert.AreEqual(request.RequestContext.LocationEndpointToRoute, ClientRetryPolicyTests.Location1Endpoint);
+
+            // Creation of 429.3092 Error.
+            HttpStatusCode throttleException = HttpStatusCode.TooManyRequests;
+            SubStatusCodes resourceNotAvailable = SubStatusCodes.SystemResourceUnavailable;
+
+            Exception innerException = new ();
+            Mock<INameValueCollection> nameValueCollection = new ();
+            DocumentClientException documentClientException = new (
+                message: "SystemResourceUnavailable: 429 with 3092 occurred.",
+                innerException: innerException,
+                statusCode: throttleException,
+                substatusCode: resourceNotAvailable,
+                requestUri: request.RequestContext.LocationEndpointToRoute,
+                responseHeaders: nameValueCollection.Object);
+
+            // Act.
+            Task<ShouldRetryResult> shouldRetry = retryPolicy.ShouldRetryAsync(
+                documentClientException,
+                new CancellationToken());
+
+            // Assert.
+            Assert.IsTrue(shouldRetry.Result.ShouldRetry);
+            retryPolicy.OnBeforeSendRequest(request);
+
+            if (isMultiMasterAccount)
+            {
+                Assert.AreEqual(
+                    expected: ClientRetryPolicyTests.Location2Endpoint,
+                    actual: request.RequestContext.LocationEndpointToRoute,
+                    message: "The request should be routed to the next region, since the accound is a multi master write account and the request" +
+                    "failed with 429.309 which got converted into 503 internally. This should trigger another retry attempt to the next region.");
+            }
+            else
+            {
+                Assert.AreEqual(
+                    expected: ClientRetryPolicyTests.Location1Endpoint,
+                    actual: request.RequestContext.LocationEndpointToRoute,
+                    message: "Since this is asingle master account, the write request should not be retried on the next region.");
+            }
+        }
 
         /// <summary>
         /// Tests to see if different 503 substatus codes are handeled correctly