Batch
User Documentation

Overview

A batch service is a service that makes it possible to run workflow jobs on a homogeneous cluster managed by a batch scheduler. The batch scheduler receives requests that ask for a number of compute nodes, with a number of cores per compute node, and a duration. Requests wait in a queue and, using a range of possible batch scheduling algorithms, are dispatched to the requested compute resources in a space-sharing manner. Therefore, a job submitted to the service experiences a "queue waiting time" period (the length of which depends on the load on the service) followed by an "execution time" period. In typical batch-scheduler fashion, a running job is terminated when it reaches its requested duration, which may cause the job to fail. If, instead, the job completes before the requested duration the job succeeds. In both cases, the job's allocated compute resources are reclaimed by the batch scheduler.

A batch service also supports so-called "pilot jobs", i.e., jobs that are submitted to the service, with requested resources and duration, but without specifying at submission time which workflow tasks/operations should be performed by the job. Instead, once the job starts it exposes to its submitter a Bare-metal service. This service is available only for the requested duration, and can be used in any manner by the submitter. This allows late binding of workflow tasks to compute resources.

Creating a batch compute service

In WRENCH, a batch service represents a compute service (wrench::ComputeService), which is defined by the wrench::BatchService class. An instantiation of a batch service requires the following parameters:

  • A hostname on which to start the service (this is the entry point to the service)
  • A list (std::vector) of hostnames (all cores and all RAM of each host is available to the batch service)
  • A scratch space size, i.e., the size in bytes of storage local to the batch service (used to store workflow files, as needed, during job executions)
  • Maps (std::map) of configurable properties (wrench::BatchServiceProperty) and configurable message payloads (wrench::BatchServiceMessagePayload)

The example below shows how to create an instance of a batch service that runs on host "Gateway" and provides access to 4 hosts (using all their cores and RAM), with 1 TiB scratch space. Furthermore, the batch scheduling algorithm is configured to the FCFS (First-Come-First-Serve):

auto batch_cs = simulation->add(
new wrench::BatchService("Gateway",
{"Node1", "Node2", "Node3", "Node4"},
pow(2,40),
{});

Bare-metal service properties

In addition to properties inherited from wrench::ComputeServiceProperty, a batch compute service supports the following properties: