NServiceBus uses defaults that ensure good performance in common cases. While this is usually the preferred mode of operation there are situations where tuning might be desired.
Examples where concurrency tuning might be relevant are:
- Non-thread-safe code that needs to run sequentially
- Databases that might deadlock when getting too many concurrent requests
max(Number of logical processors, 2).
Limit maximum concurrency so that no more messages than the specified value are ever processed at the same time. If a maximum concurrency is not specified, the transport will choose an optimal value that is a balance between throughput and effective resource usage. The concurrency limit cannot be changed at run-time and can only be applied at endpoint instance creation and requires the instance to be restarted for concurrency changes to take effect.
Infrastructure monitoring should be set up for the environment that hosts the endpoint instance (as well as any remote resources, such as databases) to monitor CPU, RAM, network, and storage to validate if a change made to the concurrency is not negatively affecting the overall system.
Set the concurrency limit value to
1 to process messages sequentially. Sequential processing is not a guarantee for ordered processing. For example, processing failures and recoverability will result in out-of-order processing.
Throughput throttling options have been deprecated. To enable throttling on Version 6 and higher, a custom behavior should be used. The throttling sample demonstrates how such a behavior can be implemented.