I read from Oozie official site: Actions Are Asynchronous

All computation/processing tasks triggered by an action node are executed asynchronously by Oozie. For most types of computation/processing tasks triggered by workflow action, the workflow job has to wait until the computation/processing task completes before transitioning to the following node in the workflow.

Whereas on different page of the same site: Fs HDFS action

The introduction of FS action (synchronous action) told that:

The FS commands are executed synchronously from within the FS action, the workflow job will wait until the specified file commands are completed before continuing to the next action.

Why synchronous and asynchronous introduction is basically the same?According to my understanding from the operating system principle course, asynchronous means the function does not wait but continue the execution.

Excerpt From: Mohammad Kamrul Islam and Aravind Srinivasan. "Apache Oozie."

Asynchronous Actions : All Hadoop actions and the <shell> action follow the "Action Execution Model". These are called asynchronous actions because they are launched via a launcher as Hadoop jobs.

Synchronous Actions : The filesystem action, email action, SSH action, and sub-workflow action are executed by the Oozie server itself and are called synchronous actions. The execution of these synchronous actions do not require running any user code—just access to some libraries.

Essentially, In both the cases Oozie server waits for the completion of the action and then only moves to the next action in the DAG. The separation is mainly based on whether actinos executes on the same Oozie server or on the Hadoop cluster.

Here is list of Oozie Actions and their Action Execution Model.