Retrieve checkpoints one by one

sdk/eventhub/Azure.Messaging.EventHubs.Processor/api/Azure.Messaging.EventHubs.Processor.netstandard2.0.cs

@@ -21,6 +21,7 @@ public EventProcessorClient(Azure.Storage.Blobs.BlobContainerClient checkpointSt
         protected override Azure.Messaging.EventHubs.EventHubConnection CreateConnection() { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public override bool Equals(object obj) { throw null; }
+        protected override System.Threading.Tasks.Task<Azure.Messaging.EventHubs.Primitives.EventProcessorCheckpoint> GetCheckpointAsync(string partitionId, System.Threading.CancellationToken cancellationToken) { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public override int GetHashCode() { throw null; }
         protected override System.Threading.Tasks.Task<System.Collections.Generic.IEnumerable<Azure.Messaging.EventHubs.Primitives.EventProcessorCheckpoint>> ListCheckpointsAsync(System.Threading.CancellationToken cancellationToken) { throw null; }

sdk/eventhub/Azure.Messaging.EventHubs.Processor/src/Diagnostics/BlobEventStoreEventSource.cs

@@ -395,5 +395,70 @@ public virtual void InvalidCheckpointFound(string partitionId,
                 WriteEvent(35, partitionId ?? string.Empty, fullyQualifiedNamespace ?? string.Empty, eventHubName ?? string.Empty, consumerGroup ?? string.Empty);
             }
         }
+
+        /// <summary>
+        ///   Indicates that an attempt to retrieve a checkpoint has started.
+        /// </summary>
+        ///
+        /// <param name="fullyQualifiedNamespace">The fully qualified Event Hubs namespace the checkpoint are associated with.  This is likely to be similar to <c>{yournamespace}.servicebus.windows.net</c>.</param>
+        /// <param name="eventHubName">The name of the specific Event Hub the checkpoint is associated with, relative to the Event Hubs namespace that contains it.</param>
+        /// <param name="consumerGroup">The name of the consumer group the checkpoint is associated with.</param>
+        /// <param name="partitionId">The partition id the specific checkpoint is associated with.</param>
+        ///
+        [Event(36, Level = EventLevel.Informational, Message = "Starting to retrieve checkpoint for FullyQualifiedNamespace: '{0}'; EventHubName: '{1}'; ConsumerGroup: '{2}'; PartitionId: '{3}'.")]
+        public virtual void GetCheckpointStart(string fullyQualifiedNamespace,
+                                        string eventHubName,
+                                        string consumerGroup,
+                                        string partitionId)
+        {
+            if (IsEnabled())
+            {
+                WriteEvent(36, fullyQualifiedNamespace ?? string.Empty, eventHubName ?? string.Empty, consumerGroup ?? string.Empty, partitionId ?? string.Empty);
+            }
+        }
+
+        /// <summary>
+        ///   Indicates that an attempt to retrieve a checkpoint has completed.
+        /// </summary>
+        ///
+        /// <param name="fullyQualifiedNamespace">The fully qualified Event Hubs namespace the checkpoint are associated with.  This is likely to be similar to <c>{yournamespace}.servicebus.windows.net</c>.</param>
+        /// <param name="eventHubName">The name of the specific Event Hub the checkpoint is associated with, relative to the Event Hubs namespace that contains it.</param>
+        /// <param name="consumerGroup">The name of the consumer group the checkpoint is associated with.</param>
+        /// <param name="partitionId">The partition id the specific checkpoint is associated with.</param>
+        ///
+        [Event(37, Level = EventLevel.Informational, Message = "Completed retrieving checkpoint for FullyQualifiedNamespace: '{0}'; EventHubName: '{1}'; ConsumerGroup: '{2}'. PartitionId: '{3}'.")]
+        public virtual void GetCheckpointComplete(string fullyQualifiedNamespace,
+                                                    string eventHubName,
+                                                    string consumerGroup,
+                                                    string partitionId)
+        {
+            if (IsEnabled())
+            {
+                WriteEvent(37, fullyQualifiedNamespace ?? string.Empty, eventHubName ?? string.Empty, consumerGroup ?? string.Empty, partitionId);
+            }
+        }
+
+        /// <summary>
+        ///   Indicates that an unhandled exception was encountered while retrieving a checkpoint.
+        /// </summary>
+        ///
+        /// <param name="fullyQualifiedNamespace">The fully qualified Event Hubs namespace the checkpoint are associated with.  This is likely to be similar to <c>{yournamespace}.servicebus.windows.net</c>.</param>
+        /// <param name="eventHubName">The name of the specific Event Hub the checkpoint is associated with, relative to the Event Hubs namespace that contains it.</param>
+        /// <param name="consumerGroup">The name of the consumer group the checkpoint is associated with.</param>
+        /// <param name="partitionId">The partition id the specific checkpoint is associated with.</param>
+        /// <param name="errorMessage">The message for the exception that occurred.</param>
+        ///
+        [Event(38, Level = EventLevel.Error, Message = "An exception occurred when retrieving checkpoint for FullyQualifiedNamespace: '{0}'; EventHubName: '{1}'; ConsumerGroup: '{2}'; PartitionId: '{3}'; ErrorMessage: '{4}'.")]
+        public virtual void GetCheckpointError(string fullyQualifiedNamespace,
+                                                 string eventHubName,
+                                                 string consumerGroup,
+                                                 string partitionId,
+                                                 string errorMessage)
+        {
+            if (IsEnabled())
+            {
+                WriteEvent(38, fullyQualifiedNamespace ?? string.Empty, eventHubName ?? string.Empty, consumerGroup ?? string.Empty, partitionId ?? string.Empty, errorMessage ?? string.Empty);
+            }
+        }
     }
 }

sdk/eventhub/Azure.Messaging.EventHubs.Processor/src/EventProcessorClient.cs

@@ -775,6 +775,43 @@ protected override async Task<IEnumerable<EventProcessorCheckpoint>> ListCheckpo
             return ProcessCheckpointStartingPositions(checkpoints);
         }
 
+        /// <summary>
+        ///   Returns a checkpoint for the Event Hub, consumer group, and partition ID associated with the
+        ///   event processor instance, so that processing for a given partition can be properly initialized.
+        /// </summary>
+        ///
+        /// <param name="partitionId">The ID of the partition for which to retrieve the checkpoint.</param>
+        /// <param name="cancellationToken">A <see cref="CancellationToken"/> instance to signal the request to cancel the processing.  This is most likely to occur when the processor is shutting down.</param>
+        ///
+        /// <returns>The checkpoint for the processor to take into account when initializing partition.</returns>
+        ///
+        /// <remarks>
+        ///   Should a partition not have a corresponding checkpoint, the <see cref="EventProcessorOptions.DefaultStartingPosition" /> will
+        ///   be used to initialize the partition for processing.
+        ///
+        ///   In the event that a custom starting point is desired for a single partition, or each partition should start at a unique place,
+        ///   it is recommended that this method express that intent by returning checkpoints for those partitions with the desired custom
+        ///   starting location set.
+        /// </remarks>
+        ///
+        protected override async Task<EventProcessorCheckpoint> GetCheckpointAsync(string partitionId, CancellationToken cancellationToken)
+        {
+            var checkpoint = await StorageManager.GetCheckpointAsync(FullyQualifiedNamespace, EventHubName, ConsumerGroup, partitionId, cancellationToken).ConfigureAwait(false);
+
+            // If there was no initialization handler, no custom starting positions
+            // could have been specified.  Return the checkpoint without further processing.
+
+            if (_partitionInitializingAsync == null)
+            {
+                return checkpoint;
+            }
+
+            // Process the checkpoints to inject mock checkpoints for partitions that
+            // specify a custom default and do not have an actual checkpoint.
+
+            return checkpoint ?? CreateCheckpointWithDefaultStartingPosition(partitionId);
+        }
+
         /// <summary>
         ///   Produces a list of the ownership assignments for partitions between each of the cooperating event processor
         ///   instances for a given Event Hub and consumer group pairing.  This method is used when load balancing to allow
@@ -1041,18 +1078,31 @@ private IEnumerable<EventProcessorCheckpoint> ProcessCheckpointStartingPositions
             {
                 if (!knownCheckpoints.Contains(partition))
                 {
-                    yield return new EventProcessorCheckpoint
-                    {
-                       FullyQualifiedNamespace = FullyQualifiedNamespace,
-                       EventHubName = EventHubName,
-                       ConsumerGroup = ConsumerGroup,
-                       PartitionId = partition,
-                       StartingPosition = PartitionStartingPositionDefaults.TryGetValue(partition, out EventPosition position) ? position : DefaultStartingPosition
-                    };
+                    yield return CreateCheckpointWithDefaultStartingPosition(partition);
                 }
             }
         }
 
+        /// <summary>
+        ///   Creates a checkpoint with a default starting position set.
+        /// </summary>
+        ///
+        /// <param name="partitionId">The partition id.</param>
+        ///
+        /// <returns>Returns an artificial checkpoint for a provided partition with a starting position set to <see cref="DefaultStartingPosition"/>.</returns>
+        ///
+        private EventProcessorCheckpoint CreateCheckpointWithDefaultStartingPosition(string partitionId)
+        {
+            return new EventProcessorCheckpoint
+            {
+                FullyQualifiedNamespace = FullyQualifiedNamespace,
+                EventHubName = EventHubName,
+                ConsumerGroup = ConsumerGroup,
+                PartitionId = partitionId,
+                StartingPosition = PartitionStartingPositionDefaults.TryGetValue(partitionId, out EventPosition position) ? position : DefaultStartingPosition
+            };
+        }
+
         /// <summary>
         ///   Invokes a specified action only if this <see cref="EventProcessorClient" /> instance is not running.
         /// </summary>

sdk/eventhub/Azure.Messaging.EventHubs.Processor/src/Storage/BlobsCheckpointStore.Diagnostics.cs

@@ -224,5 +224,42 @@ partial void ClaimOwnershipStart(string partitionId, string fullyQualifiedNamesp
         ///
         partial void BlobsCheckpointStoreCreated(string typeName, string accountName, string containerName) =>
             Logger.BlobsCheckpointStoreCreated(typeName, accountName, containerName);
+
+        /// <summary>
+        ///   Indicates that an attempt to retrieve a checkpoint has started.
+        /// </summary>
+        ///
+        /// <param name="fullyQualifiedNamespace">The fully qualified Event Hubs namespace the checkpoint are associated with.  This is likely to be similar to <c>{yournamespace}.servicebus.windows.net</c>.</param>
+        /// <param name="eventHubName">The name of the specific Event Hub the checkpoint is associated with, relative to the Event Hubs namespace that contains it.</param>
+        /// <param name="consumerGroup">The name of the consumer group the checkpoint is associated with.</param>
+        /// <param name="partitionId">The partition id the specific checkpoint is associated with.</param>
+        ///
+        partial void GetCheckpointStart(string fullyQualifiedNamespace, string eventHubName, string consumerGroup, string partitionId) =>
+            Logger.GetCheckpointStart(fullyQualifiedNamespace, eventHubName, consumerGroup, partitionId);
+
+        /// <summary>
+        ///   Indicates that an attempt to retrieve a checkpoint has completed.
+        /// </summary>
+        ///
+        /// <param name="fullyQualifiedNamespace">The fully qualified Event Hubs namespace the checkpoint are associated with.  This is likely to be similar to <c>{yournamespace}.servicebus.windows.net</c>.</param>
+        /// <param name="eventHubName">The name of the specific Event Hub the checkpoint is associated with, relative to the Event Hubs namespace that contains it.</param>
+        /// <param name="consumerGroup">The name of the consumer group the checkpoint is associated with.</param>
+        /// <param name="partitionId">The partition id the specific checkpoint is associated with.</param>
+        ///
+        partial void GetCheckpointComplete(string fullyQualifiedNamespace, string eventHubName, string consumerGroup, string partitionId) =>
+            Logger.GetCheckpointComplete(fullyQualifiedNamespace, eventHubName, consumerGroup, partitionId);
+
+        /// <summary>
+        ///   Indicates that an unhandled exception was encountered while retrieving a checkpoint.
+        /// </summary>
+        ///
+        /// <param name="fullyQualifiedNamespace">The fully qualified Event Hubs namespace the checkpoint are associated with.  This is likely to be similar to <c>{yournamespace}.servicebus.windows.net</c>.</param>
+        /// <param name="eventHubName">The name of the specific Event Hub the checkpoint is associated with, relative to the Event Hubs namespace that contains it.</param>
+        /// <param name="consumerGroup">The name of the consumer group the checkpoint is associated with.</param>
+        /// <param name="partitionId">The partition id the specific checkpoint is associated with.</param>
+        /// <param name="exception">The message for the exception that occurred.</param>
+        ///
+        partial void GetCheckpointError(string fullyQualifiedNamespace, string eventHubName, string consumerGroup, string partitionId, Exception exception) =>
+            Logger.GetCheckpointError(fullyQualifiedNamespace, eventHubName, consumerGroup, partitionId, exception.Message);
     }
 }