Wednesday, November 13, 2019

MassTransit–Batch Message Consumption

A lesser known feature inside MassTransit is the support of batch messages. This can be a really nice feature if you want to combine a batch of high-volume smaller messages into a single atomic consumer.

How does this work?

MassTransit will combine multiple messages into a single consume by specifying a window, such as a message count (batch size), time period, or a combination of both.

There are 2 configurable limits:

  • Size: A limit specifying the maximum number of messages which can fit into a single batch will trigger once that many messages are ready to be consumed. The batch size must be less than or equal to any prefetch counts or concurrent message delivery limits in order reach the size limit.

  • Time: A limit specifying how long to wait for additional messages from the time when the first message is ready, after which the messages ready within that time are delivered as a single batch. The time limit should be well within the lock time of a message, including enough time to process the batch.

Batch configuration

To use the batching functionality, configure an extra receive endpoint and use the Batch method to configure the endpoint:

Batch consumption

The message batch is delivered as an array to the consumer, so that the existing behavior is maintained for middleware, factories, etc. An additional context is available on the payload, which can be used to discover details related to the batch. Instead of receiving a single message you get a Batch<T> of messages:

Remark: This feature is experimental.  Be sure to configure the transport with sufficient concurrent message capacity (prefetch, etc.) so that a batch can actually complete without always reaching the time limit.