Support for Batch sending

[TsengSR]

I've been wondering whether or not the messages are sent as batch, when using a transaction and ended up here

Rebus.RabbitMq/Rebus.RabbitMq/RabbitMq/RabbitMqTransport.cs

Lines 729 to 735 in 2320f64

	model.BasicPublish(
	exchange: exchange,
	routingKey: routingKey.RoutingKey,
	mandatory: mandatory,
	basicProperties: props,
	body: message.Body
	);

From what I understand is, that even though the acknowledges are batched (model.ConfirmSelect()), the messages itself aren't batched, right?

In my research I at least found out that some transport may support that and RabbitMQ is one of them according to this PR rabbitmq/rabbitmq-dotnet-client#368

I wonder if we could have that in RabbitMQ Transport too, preferably as opt-in feature. It's not purely for performance, its more that'd I'd prefer to have either all or none messages being accepted by RabbitMQ rather than having half of them submitted/confirmed and the other half failing when the connection drops or similar.

It doesn't necessary need a public API for batching, just adding it to the transport and using it if the feature been enabled when confirming the message scope

[mookid8000]

Oh, I didn't know that the RabbitMQ driver had added a batching API.

It should be fairly straightforward to have Rebus use that when it's relevant to do so,.

PRs are most welcome 🤗 otherwise sit tight and wait – I will fix this some time in the future.

[mookid8000]

With Rebus.RabbitMq 9.2.0 it is now possible to enable batching by doing something like this in the configuration:

services.AddRebus(
    configure => configure
        .Transport(t => t.UseRabbitMq(connectionString, queueName)
            .SetBatchSize(100))
);

which will make Rebus use the driver's built-in ability to batch commands when possible.

When enabled, Rebus will automatically batch all messages sent/published from inside Rebus handlers or from RebusTransactionScopes.

Please note that it might not always be beneficial to enable batching. E.g. a few tests run with a RabbitMQ running in a local Docker container revealed no benefit from enabling batching. This might be different when using a RabbitMQ that is hosted on a different server or with a slower network.