The SQL Server transport supports [delayed delivery]/nservicebus/messaging/delayed-delivery.md) by storing the delayed messages in a dedicated table. When a message delay time lapses, SQL Server transport moves messages to the destination queues in batches. Note that this means the exact time of delivering a delayed message is always an approximation.
The native delayed delivery feature of the SQL Server transport is not available to send-only endpoints.
Configuration
The settings described in this section have default values as shown in the snippets. The settings can be fine-tuned to fit a particular system's needs, e.g. messages are checked for expiration more frequently resulting in more accurate delivery times.
Native delayed delivery mechanism has been introduced in version 3 of the transport. Older endpoints that use Timeout Manager can be migrated to the new mechanism by following the upgrade guide.
Table suffix
Delayed messages are stored in a dedicated table named endpoint-name.. The suffix is set to Delayed by default, but can be overwritten using:
delayedDeliverySettings.TableSuffix("Delayed");
Batch size
The SQL Server transport processes delayed messages in batches. Each time the transport queries for messages, it will use the batch size setting to limit the number of messages to be processed. This batch size is set to 100 by default, but can be configured using:
delayedDeliverySettings.BatchSize(100);
Backwards compatibility
When upgrading to a version of the transport that supports native delayed delivery, it is safe to run a set of endpoints that include both endpoints using native delayed delivery as well as the timeout manager:
- Endpoints with native delayed delivery can send delayed messages to endpoints using the timeout manager.
- Endpoints with native delayed delivery can continue to receive delayed messages from endpoints using timeout manager.
Enable the timeout manager
To assist with the upgrade process when upgrading from an older version of the transport that doesn't support native-delayed delivery, the timeout manager can be enabled. Any delayed messages stored in the endpoint's persistence database before the upgrade are sent when their timeouts expire. Any delayed messages sent after the upgrade are sent through the native delayed delivery infrastructure, even though the timeout manager is enabled. The timeout manager migration mode can be enabled with:
delayedDeliverySettings.EnableTimeoutManagerCompatibility();
Once an endpoint has no more delayed messages in its persistence database, there is no need for the timeout manager. It can be disabled by removing the above enable call.
At this point, all . and . tables for the endpoint can be deleted from the database. In addition, the endpoint no longer requires timeout persistence, so those storage entities can be removed from the persistence database as well.
Timeout Manager should also be disabled for newly created endpoints, i.e. endpoints that use the native delayed delivery implementation and haven't been deployed yet.