Adding ETag Usage to the Instance Table

src/DurableTask.AzureStorage/AzureStorageOrchestrationService.cs

@@ -1230,7 +1230,7 @@ await this.CommitOutboundQueueMessages(
             // will result in a duplicate replay of the orchestration with no side-effects.
             try
             {
-                session.ETag = await this.trackingStore.UpdateStateAsync(runtimeState, workItem.OrchestrationRuntimeState, instanceId, executionId, session.ETag, session.TrackingStoreContext);
+                await this.trackingStore.UpdateStateAsync(runtimeState, workItem.OrchestrationRuntimeState, instanceId, executionId, session.ETags, session.TrackingStoreContext);
                 // update the runtime state and execution id stored in the session
                 session.UpdateRuntimeState(runtimeState);
 

src/DurableTask.AzureStorage/AzureStorageOrchestrationServiceSettings.cs

@@ -294,5 +294,22 @@ internal LogHelper Logger
         /// The default is <see cref="QueueClientMessageEncoding.UTF8"/>.
         /// </summary>
         public QueueClientMessageEncoding QueueClientMessageEncoding { get; set; } = QueueClientMessageEncoding.UTF8;
+
+        /// <summary>
+        /// When true, an etag is used when attempting to make instance table updates upon completing an orchestration work item.
+        /// </summary>
+        /// <remarks>
+        /// By default, etags are only used when updating the history table upon completing an orchestration work item. This can lead 
+        /// to subtle race conditions where the instance table is incorrectly updated. Consider the following scenario:
+        /// 1. Worker A completes an orchestration work item, sends outgoing messages, updates the history table, then stalls.
+        /// 2. Worker B picks up the next and final orchestration work item for the same instance and completes it, updating the history 
+        /// table and instance table with the new terminal status.
+        /// 3. Worker A resumes and overrides the terminal status in the instance table with an incorrect non-terminal status.
+        /// This will leave the instance status of the orchestration permanently as "Running" even though it has actually completed.
+        /// To prevent such scenarios, enabling this setting will ensure that instance table updates also use etags. This would prevent
+        /// worker A's update in step 3 from completing. Enabling this setting will also introduce a performance overhead since the instance
+        /// table must now be read before processing every orchestration work item to obtain the latest etag.
+        /// </remarks>
+        public bool UseInstanceTableEtag { get; set; } = false;
     }
 }

src/DurableTask.AzureStorage/MessageData.cs

@@ -111,6 +111,8 @@ internal void Update(UpdateReceipt receipt)
         {
             this.OriginalQueueMessage = this.OriginalQueueMessage.Update(receipt);
         }
+
+        internal object MessageMetadata { get; set; }
     }
 
     /// <summary>

src/DurableTask.AzureStorage/Messaging/OrchestrationSession.cs

@@ -37,7 +37,7 @@ public OrchestrationSession(
             ControlQueue controlQueue,
             List<MessageData> initialMessageBatch,
             OrchestrationRuntimeState runtimeState,
-            ETag? eTag,
+            OrchestrationETags eTags,
             DateTime lastCheckpointTime,
             object trackingStoreContext,
             TimeSpan idleTimeout,
@@ -48,7 +48,7 @@ public OrchestrationSession(
             this.ControlQueue = controlQueue ?? throw new ArgumentNullException(nameof(controlQueue));
             this.CurrentMessageBatch = initialMessageBatch ?? throw new ArgumentNullException(nameof(initialMessageBatch));
             this.RuntimeState = runtimeState ?? throw new ArgumentNullException(nameof(runtimeState));
-            this.ETag = eTag;
+            this.ETags = eTags;
             this.LastCheckpointTime = lastCheckpointTime;
             this.TrackingStoreContext = trackingStoreContext;
 
@@ -66,7 +66,7 @@ public OrchestrationSession(
 
         public OrchestrationRuntimeState RuntimeState { get; private set; }
 
-        public ETag? ETag { get; set; }
+        public OrchestrationETags ETags { get; set; }
 
         public DateTime LastCheckpointTime { get; }
 

src/DurableTask.AzureStorage/OrchestrationETags.cs

@@ -0,0 +1,24 @@
+//  ----------------------------------------------------------------------------------
+//  Copyright Microsoft Corporation
+//  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.
+//  ----------------------------------------------------------------------------------
+#nullable enable
+namespace DurableTask.AzureStorage
+{
+    using Azure;
+
+    class OrchestrationETags
+    {
+        internal ETag? InstanceETag { get; set; }
+
+        internal ETag? HistoryETag { get; set; }
+    }
+}

src/DurableTask.AzureStorage/OrchestrationSessionManager.cs

@@ -271,21 +271,25 @@ async Task<IEnumerable<MessageData>> DedupeExecutionStartedMessagesAsync(
             // Terminology:
             // "Local"  -> the instance ID info comes from the local copy of the message we're examining
             // "Remote" -> the instance ID info comes from the Instances table that we're querying
-            IAsyncEnumerable<OrchestrationState> instances = this.trackingStore.GetStateAsync(instanceIds, cancellationToken);
-            IDictionary<string, OrchestrationState> remoteOrchestrationsById = 
-                await instances.ToDictionaryAsync(o => o.OrchestrationInstance.InstanceId, cancellationToken);
+            IAsyncEnumerable<InstanceStatus> instances = this.trackingStore.FetchInstanceStatusAsync(instanceIds, cancellationToken);
+            IDictionary<string, InstanceStatus> remoteOrchestrationsById = 
+                await instances.ToDictionaryAsync(o => o.State.OrchestrationInstance.InstanceId, cancellationToken);
 
             foreach (MessageData message in executionStartedMessages)
             {
                 OrchestrationInstance localInstance = message.TaskMessage.OrchestrationInstance;
                 var expectedGeneration = ((ExecutionStartedEvent)message.TaskMessage.Event).Generation;
-                if (remoteOrchestrationsById.TryGetValue(localInstance.InstanceId, out OrchestrationState remoteInstance) &&
-                    (remoteInstance.OrchestrationInstance.ExecutionId == null || string.Equals(localInstance.ExecutionId, remoteInstance.OrchestrationInstance.ExecutionId, StringComparison.OrdinalIgnoreCase)))
+                if (remoteOrchestrationsById.TryGetValue(localInstance.InstanceId, out InstanceStatus remoteInstance) &&
+                    (remoteInstance.State.OrchestrationInstance.ExecutionId == null || string.Equals(localInstance.ExecutionId, remoteInstance.State.OrchestrationInstance.ExecutionId, StringComparison.OrdinalIgnoreCase)))
                 {
                     // Happy path: The message matches the table status. Alternatively, if the table doesn't have an ExecutionId field (older clients, pre-v1.8.5),
                     // then we have no way of knowing if it's a duplicate. Either way, allow it to run.
+                    if (this.settings.UseInstanceTableEtag)
+                    {
+                        message.MessageMetadata = remoteInstance.ETag;
+                    }
                 }
-                else if (expectedGeneration == remoteInstance?.Generation && this.IsScheduledAfterInstanceUpdate(message, remoteInstance))
+                else if (expectedGeneration == remoteInstance?.State.Generation && this.IsScheduledAfterInstanceUpdate(message, remoteInstance?.State))
                 {
                     // The message was scheduled after the Instances table was updated with the orchestration info.
                     // We know almost certainly that this is a redundant message and can be safely discarded because
@@ -476,6 +480,10 @@ internal void AddMessageToPendingOrchestration(
                     if (targetBatch == null)
                     {
                         targetBatch = new PendingMessageBatch(controlQueue, instanceId, executionId);
+                        if (this.settings.UseInstanceTableEtag && data.MessageMetadata is ETag instanceEtag)
+                        {
+                            targetBatch.ETags.InstanceETag = instanceEtag;
+                        }
                         node = this.pendingOrchestrationMessageBatches.AddLast(targetBatch);
 
                         // Before the batch of messages can be processed, we need to download the latest execution state.
@@ -519,9 +527,20 @@ async Task ScheduleOrchestrationStatePrefetch(
                        cancellationToken);
 
                     batch.OrchestrationState = new OrchestrationRuntimeState(history.Events);
-                    batch.ETag = history.ETag;
+                    batch.ETags.HistoryETag = history.ETag;
                     batch.LastCheckpointTime = history.LastCheckpointTime;
                     batch.TrackingStoreContext = history.TrackingStoreContext;
+
+                    // Try to get the instance ETag from the tracking store if it wasn't already provided
+                    if (this.settings.UseInstanceTableEtag && batch.ETags.InstanceETag == null)
+                    {
+                        InstanceStatus? instanceStatus = await this.trackingStore.FetchInstanceStatusAsync(
+                            batch.OrchestrationInstanceId,
+                            cancellationToken);
+                        // The instance could not exist in the case that these messages are for the first execution of a suborchestration,
+                        // or an entity-started orchestration, for example
+                        batch.ETags.InstanceETag = instanceStatus?.ETag;
+                    }
                 }
 
                 if (this.settings.UseSeparateQueueForEntityWorkItems
@@ -590,7 +609,7 @@ async Task ScheduleOrchestrationStatePrefetch(
                             nextBatch.ControlQueue,
                             nextBatch.Messages,
                             nextBatch.OrchestrationState,
-                            nextBatch.ETag,
+                            nextBatch.ETags,
                             nextBatch.LastCheckpointTime,
                             nextBatch.TrackingStoreContext,
                             this.settings.ExtendedSessionIdleTimeout,
@@ -737,8 +756,10 @@ public OrchestrationRuntimeState? OrchestrationState
                 }
             }
 
-            public ETag? ETag { get; set; }
+            public OrchestrationETags ETags { get; } = new OrchestrationETags();
+
             public DateTime LastCheckpointTime { get; set; }
+
             public object? TrackingStoreContext { get; set; }
         }
     }

src/DurableTask.AzureStorage/Storage/Table.cs

@@ -86,16 +86,18 @@ public async Task DeleteEntityAsync<T>(T tableEntity, ETag ifMatch = default, Ca
             this.stats.TableEntitiesWritten.Increment();
         }
 
-        public async Task InsertEntityAsync<T>(T tableEntity, CancellationToken cancellationToken = default) where T : ITableEntity
+        public async Task<Response> InsertEntityAsync<T>(T tableEntity, CancellationToken cancellationToken = default) where T : ITableEntity
         {
-            await this.tableClient.AddEntityAsync(tableEntity, cancellationToken).DecorateFailure();
+            Response result = await this.tableClient.AddEntityAsync(tableEntity, cancellationToken).DecorateFailure();
             this.stats.TableEntitiesWritten.Increment();
+            return result;
         }
 
-        public async Task MergeEntityAsync<T>(T tableEntity, ETag ifMatch, CancellationToken cancellationToken = default) where T : ITableEntity
+        public async Task<Response> MergeEntityAsync<T>(T tableEntity, ETag ifMatch, CancellationToken cancellationToken = default) where T : ITableEntity
         {
-            await this.tableClient.UpdateEntityAsync(tableEntity, ifMatch, TableUpdateMode.Merge, cancellationToken).DecorateFailure();
+            Response result = await this.tableClient.UpdateEntityAsync(tableEntity, ifMatch, TableUpdateMode.Merge, cancellationToken).DecorateFailure();
             this.stats.TableEntitiesWritten.Increment();
+            return result;
         }
 
         public async Task InsertOrMergeEntityAsync<T>(T tableEntity, CancellationToken cancellationToken = default) where T : ITableEntity