A virtual node is a control node that does not generate any data. Generally, it is used as the root node of overall planning nodes in the workflow.
The final output table of a workflow contains multiple branch input tables. Virtual nodes are usually used if these input tables are not dependent.
An output table is generated after the source tables imported by three data synchronization tasks are processed by the ODPS_SQL task. The three data synchronization tasks are not dependent, but the ODPS_SQL task is dependent on the three data synchronization tasks. The workflow is shown as follows.
A virtual node is used as the root node where the workflow starts. The three data synchronization tasks depend on the virtual node and the ODPS_SQL processing task is dependent on the three data synchronization tasks.
On the Data Development page, click New and select Create Task.
Complete the configurations in the Create Task dialog box.
Select Workflow Task as the task type and Periodic Scheduling as the scheduling type.
Click Create to redirect to the workflow designer page.
Double-click Virtual in Nodes list.
After entering the node name, click Create to obtain the following virtual nodes.
The workflow dataworks1 was created in the previous section, so only one virtual node task is in the workflow.
Click Test Run.
Click OK in the Running Reminder for Periodic Tasks dialog box.
Click Run in the Test Run dialog box.
Click Go to O&M Center in the Workflow Task Test Run dialog box.
Double-click the workflow name to enter the workflow.
Then, you can see the running status of the nodes in the workflow.
Click the virtual node, and select Operation Log.
Task log prompt: No data.
Reason: The virtual node task is set as running successfully when the virtual node runs but does not run actually, so the task does not generate any log information.