MassTransit - How to fault messages in a batch

Question

I am trying to utilize the MassTransit batching technique to process multiple messages to reduce the individual queries to be database (read and write). If there is an exception while processing one/more of the messages, then the expectation is to fault only required messages and have the ability to process the rest of the messages.

This is common scenario in my use case ,what I am trying to establish here is a way to perform batch processing that caters for poisoned messages

For example, if I have a batch size of 10 messages, 10 in the queue and 1 persistently fails, I still need a means of ensuring the other 9 can be processed successfully. It is fine if all 10 need to be returned to the queue and subset re-consumed - but the poisoned message needs to be eliminated somehow. Does this requirement discount the use of batching?

I have tried below, however did solve my use case.

1. catching the exception and raising NotifyFaulted for that specific message.

modified sample-twitch application, to throw an exception to something like below , based on https://github.com/MassTransit/Sample-Twitch/blob/master/src/Sample.Components/BatchConsumers/RoutingSlipBatchEventConsumer.cs file.

   public Task Consume(ConsumeContext<Batch<RoutingSlipCompleted>> context)
    {
        if (_logger.IsEnabled(LogLevel.Information))
        {
            _logger.Log(LogLevel.Information, "Routing Slips Completed: {TrackingNumbers}",
                string.Join(", ", context.Message.Select(x => x.Message.TrackingNumber)));
        }

        for (int i = 0; i < context.Message.Length; i++)
        {
            try
            {
                if (i % 2 != 0)
                    throw new System.Exception("business error -message failed");
            }
            catch (System.Exception ex)
            {
                context.Message[i].NotifyFaulted(TimeSpan.Zero, "batch routing silp faulted", ex);
            }
           
        }
        return Task.CompletedTask;
    }

I have dig into a few more threads that look similar to the issue ,for reference. Masstransit error handling for batch consumer

Answer 1

If you want to use batch, and have a message in that batch that cannot be processed, you should catch the exception and do something else with the poison message. You could write it someplace else, publish some type of event, or whatever else. But MassTransit does not allow you to partially complete/fault messages of a batch.