This page refers to the legacy Azure Service Bus transport that uses the WindowsAzure.ServiceBus NuGet package. This package is currently on extended support until May 2022, after which it will be out of support according to the support policy. All users should migrate to the Azure Service Bus transport transport.

Batching store access

In order to increase message throughput, the Azure Service Bus batches operations prior to writing to its internal store. This involves delaying write operations by 20 ms. Read operations are not affected.

Batching store operations should be disabled for low throughput scenarios requiring low latency.

Batching store operations is enabled by default. In order to disable it, set EnableBatching(false) on queues, topics, and subscriptions.

Client-side batching

Client-side batching allows messages, being sent to a queue or topic, to be delayed for a short period of time. Additional messages sent to the same queue or topic within the specified time period will be grouped and transmitted together in a single batch. This setting affects the Azure Service Bus Message Senders and can be configured using BatchFlushInterval. Client-side batching is enabled by default.

Batching store operations should be disabled for low throughput scenarios requiring low latency. To do so, set the BatchFlushInterval to TimeSpan.Zero. For high-throughput scenarios, increase the BatchFlushInterval.

Batched store access is only available for asynchronous Send and Complete operations. Synchronous operations are immediately sent to the Service Bus service. Batching does not occur for Peek or Receive operations, nor does batching occur across clients.

Batching messages sent from a handler

Azure Service Bus optimizes multiple message sends from a handler by batching send operations into a single operation. For example, when a handler is sending multiple messages, Azure Service Bus will batch those and send in as few operations as possible. The size of a batch cannot exceed the maximum size on a BrokeredMessage. The maximum message size is configured using MaximumMessageSizeInKilobytes setting of the Message Senders.

BrokeredMessage size is different between tiers of Azure Service Bus.

The batch size that can be sent from within a handler also depends on the TransportTransactionMode.

When TransportTransactionMode.SendsAtomicWithReceive is used, Azure Service Bus limits number of outgoing operations from a handler context to 100. If the number of outgoing operations exceeds the limit, TransactionContainsTooManyMessages exception will be thrown and incoming message will be eventually moved to the error queue. To send more than 100 outgoing operations, lower transport transaction mode.

When batching messages sent from a handler, the underlying implementation of batching serializes messages. A serialized batch is usually bigger than the original messages combined. To ensure successful batch sending operation, the batch should not exceed the BrokeredMessage size. To cater for the overhead caused by serialization, the final batch size is estimated using MessageSizePaddingPercentage setting. By default, it's set to 5%. It can be configured using MessageSizePaddingPercentage configuration of the Message Senders.

By default, message batches exceeding the maximum allowed size by Azure Service Bus, will throw a MessageTooLargeException. The default behavior can by changed with OversizedBrokeredMessageHandler<T>(T) configuration of the Message Senders.

Padding and estimated batch size calculation

The following are taken into consideration for batch size calculation:

  • Raw body size in bytes.
  • Custom headers size (keys and values) in bytes.
  • Estimated standard properties size in bytes. For string properties, assumed size is 256 bytes.
  • Additional MessageSizePaddingPercentage to account for serialization and internals added by Azure Service Bus library upon sending.

The default value for MessageSizePaddingPercentage is 5%. The custom percentage might be required when dealing with consistent size pattern messages. Tables below demonstrate 5% padding and its affect on the message size estimate for various payload sizes.

BrokeredMessageBodyType set to SupportedBrokeredMessageBodyTypes.ByteArray. MessageSizePaddingPercentage set to 5%

Single message payload sizeSize reported by the brokerEstimated (padded) sizeIncrease

BrokeredMessageBodyType set to SupportedBrokeredMessageBodyTypes.Stream. MessageSizePaddingPercentage set to 5%

Single message payload sizeSize reported by the brokerEstimated (padded) sizeIncrease

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