What does the persistence subsystem do?
The persistence subsystem is responsible for making a workflow instance durable. Durable workflow instances can be unloaded from memory and reloaded on the same or a different machine at a later point in time. This way, the persistence subsystem enables scenarios such as long-running workflow applications, increase system load by unloading idle instance, migration of instances between machines, scale out and load-balancing, and recovery of failed instances.
· Storing the state of workflow instances in a persistence store.
· Recovery of durable workflow instances.
· Activation of durable workflow instances with expired durable timers.
· Instantaneous reactivation of durable workflow instances after a shutdown or crash of the Workflow Service Host.
· Some activities persist the instance. The SendReplyToReceive activityhas a PersistBeforeSend property, which can be set to persist the Workflow state before a reply is sent.
· The user defines the Workflow Idle behavior and sets the PersistOnIdle time. When specified the Workflow Service Host persists the instance after the instance has been idle for the specified time. An instance can go idle when it is waiting on a receive or delay activity.
· The user defines the Workflow Idle behavior and sets the UnloadOnIdle time. When specified the Workflow Service Host persists and unloads the instance after the instance has been idle for the specified time.