Combining

Combining, or "fan in", is used to refer to a step Job that expects multiple input files and creates a single output file. Simple concatenation of the files is one example. "Combiner" Jobs typically join a large number of files (produced by a prior parallel step) in a single step instance.

The Workflow Engine determines that a step is combining multiple files by inspecting the plumbing that refers to a prior steps's output. If a step input variable is (according to the Job Definition) of type files then the step is assumed to be a combiner of files generated by multiple instances of a prior step.