HOWTO14 How to use COMPSs

 COMPSs is a programming framework, composed of a programming model and an execution runtime which supports it, whose main objective is to ease the development of applications for distributed environments. On the one hand, the COMPSs programming model aims to keep the programmers unaware of the execution environment and parallelization details. 

On the other hand, the COMPSs runtime is in charge of optimizing the performance of the application by exploiting its inherent concurrency. The runtime intercepts any call to a selected method creating a representative task and finding the data dependencies with all the previous ones that must be considered along the application run. 

Through the monitoring of the workload of the application, the runtime determines the excess/lack of resources and turns to cloud providers enforcing a dynamic management of the resource pool. In order to make COMPSs interoperable with different providers, a common interface is used, which implements the specific cloud provider API. Currently, there exist connectors for Amazon EC2, Azure and for providers that implement the Open Cloud Computing Interface (OCCI) and the Open Virtualization Format (OVF) specifications for resource management.

The COMPSs PMES

The Programming Model Enactment Service (PMES) is a web service that allows the execution of applications programmed through the COMPSs programming model. A client is used to contact an OGF BES compliant endpoint in order to submit the execution of the application. This request is expressed through a JSDL document containing the application name, the input parameters and data references. When a request is received, a virtual machine is requested to the Cloud Provider in order to deploy the application downloading its package from a storage location. Once the runtime machine is deployed the COMPSs application is remotely started. In its turn, the COMPSs runtime will schedule the tasks on a set of machines created on demand. This phase includes the staging of input files from remote locations as specified in the execution request. The COMPSs-PMES service can be also configured to boot a predefined number of VMs on the provider where the service is deployed; this solution allows the serving of requests that involve the execution of smaller operations in a reasonable time avoiding the overhead of VM creation; if the number of requests exceeds the available resources, the service is still able to dynamically deploy new instances in order to cope with the burst of load.