Apache Spark Certification Practice Test

An action in Apache Spark is an operation that triggers the execution of the computation from a Spark job and returns a value to the driver program. The primary purpose of an action is to bring data from the distributed environment back to a single location or trigger side effects, such as writing to external storage.

"Collect" is an example of an action because it retrieves all elements of the dataset (or RDD) and brings them to the driver as an array. When you call collect, Spark runs the transformations that had been defined on that dataset and fetches the final results. This is essential for cases where you need to review data or perform operations that require the entire result set to be available on the driver.

In contrast, operations like "Map," "Filter," and "Join" are considered transformations. These methods return a new dataset derived from the original dataset but do not trigger the execution of the transformations themselves. The transformations construct a logical plan that Spark will execute later when an action is called. This distinction between actions and transformations is fundamental in understanding how Spark processes data.