1. Introduction

RADICAL-Pilot is a Pilot Job system written in Python. It allows a user to run large numbers of computational tasks (called ComputeUnits) concurrently on one or more remote ComputePilots that RADICAL-Pilot can start transparently on a multitude of different distributed resources, like HPC clusters and Clouds.

In this model, the resource is acquired by a user’s application so that the application can schedule ComputeUnits into that resource directly, rather than going through the system’s job scheduler.

In many cases, this can drastically shorten overall exeuction time as the individual ComputeUnits don’t have to wait in the system’s scheduler queue but can execute directly on the ComputePilots.

ComputeUnits are often single-core / multi-threaded executables, but SAGA- Pilot also supports execution of parallel executables, for example based on MPI or OpenMP.

RADICAL-Pilot is not a static system, but it rather provides the user with a programming library (“Pilot-API”) that provides abstractions for resource access and task management. With this library, the user can develop everything from simple “submission scripts” to arbitrarily complex applications, higher- level services and tools.