How to: Enable Persistence for Workflows and Workflow Services

This topic describes how to enable persistence for workflows and workflow services.

Enable Persistence for Workflows

You can associate an instance store with a WorkflowApplication by using the InstanceStore property of the WorkflowApplication class. The Persist method saves or persists a workflow into the instance store associated with the application. The Unload method persists a workflow into the instance store and then unloads the instance from the memory. The Load method loads a workflow into memory using the workflow data stored in the instance persistence store.

The Persist method performs the following steps:

1. Pauses the workflow scheduler and waits until the workflow enters the idle state.

2. Persists or saves the workflow into the persistence store.

3. Resumes the workflow scheduler.

The Unload method performs the following steps:

1. Pauses the workflow scheduler and waits until the workflow enters the idle state.

2. Persists or saves the workflow into the persistence store.

3. Disposes the workflow instance in the memory.

Both the Persist and Unload methods will block while a workflow is in a no-persist zone until the workflow exits the no-persist zone. The method continues with the persist or unload operation after the no-persist zone completes. If the no-persist zone does not complete before the time-out elapses, or if the persistence process takes too long, a TimeoutException will be thrown.

Enable Persistence for Workflow Services in Code

The DurableInstancingOptions member of the WorkflowServiceHost class has a property named InstanceStore that you can use to associate an instance store with the WorkflowServiceHost.

// wsh is an instance of WorkflowServiceHost class
wsh.DurableInstancingOptions.InstanceStore = new SqlWorkflowInstanceStore();

When the WorkflowServiceHost is opened, persistence is automatically enabled if the DurableInstancingOptions.InstanceStore is not null.

Typically, a service behavior provides the concrete instance store to be used with a workflow service host by using the InstanceStore property. For example, the SqlWorkflowInstanceStoreBehavior creates an instance of the SqlWorkflowInstanceStore, configures it, and assigns it to the DurableInstancingOptions.InstanceStore.

Enable Persistence for Workflow Services Using an Application Configuration File

Persistence can be enabled using an application configuration file by adding the following code to your app.config or web.config file:

<configuration>
  <system.serviceModel>
    <behaviors>
      <serviceBehaviors>
        <behavior name="myBehavior">
          <sqlWorkflowInstanceStore connectionString="Data Source=myDatabaseServer;Initial Catalog=myPersistenceDatabase" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
  </system.serviceModel>
</configuration>