The Grid Engine job scheduling system is used to manage and control the resources available to computational tasks. The job scheduler considers each job's resource requests (memory, disk space, processor cores) and executes it as those resources become available. The order in which jobs are submitted and a scheduling priority also dictate how soon the job will be eligible to execute. The job scheduler may suspend (and later restart) some jobs in order to more quickly complete jobs with higher scheduling priority.

Without a job scheduler, a cluster user would need to manually search for the resources required by his or her job, perhaps by randomly logging-in to nodes and checking for other users' programs already executing thereon. The user would have to "sign-out" the nodes he or she wishes to use in order to notify the other cluster users of resource availability¹⁾. A computer will perform this kind of chore more quickly and efficiently than a human can, and with far greater sophistication.

An outdated but still mostly relevant description of Grid Engine and job scheduling can be found in the first chapter of the Sun N1™ Grid Engine 6.1 User's Guide.

In this context, a job consists of:

• a sequence of commands to be executed
• a list of resource requirements and other properties affecting scheduling of the job
• a set of environment variables

For an interactive job, the user manually types the sequence of commands once the job is eligible for execution. If the necessary resources for the job are not immediately available, then the user must wait; when resources are available, the user must be present at his/her computer in order to type the commands. Since the job scheduler does not care about the time of day, this could happen anytime, day or night.

By comparison, a batch job does not require the user be awake and at his or her computer: the sequence of commands is saved to a file, and that file is given to the job scheduler. A file containing a sequence of shell commands is also known as a script, so in order to run batch jobs a user must become familiar with shell scripting. The benefits of using batch jobs are significant:

• a job script can be reused (versus repeatedly having to type the same sequence of commands for each job)
• when resources are granted to the job it will execute immediately (day or night), yielding increased job throughput

An individual's increased job throughput is good for all users of the cluster!

At its most basic, a queue represents a collection of computing entities (call them nodes) on which jobs can be executed. Each queue has properties that restrict what jobs are eligible to execute within it: a queue may not accept interactive jobs; a queue may place an upper limit on how long the job will be allowed to execute or how much memory it can use; or specific users may be granted or denied permission to execute jobs in a queue.

When submitting a job to Grid Engine, a user can explicitly specify which queue to use: doing so will place that queue's resource restrictions (e.g. maximum execution time, maximum memory) on the job, even if they are not appropriate. Usually it is easier if the user specifies what resources his or her job requires and lets Grid Engine choose an appropriate queue.

A job scheduling system is used to manage and control the computing resources for all jobs submitted to a cluster. This includes load balancing, limiting resources, reconciling requests for memory and processor cores with availability of those resources, suspending and restarting jobs, and managing jobs with different priorities.

Each investing-entity's group (workgroup) has owner queues that allow the use a fixed number of slots to match the total number of cores purchased. If a job is submitted that would use more than the slots allowed, the job will wait until enough slots are made available by completed jobs. There is no time limit imposed on owner queue jobs. All users can see running and waiting jobs, which allows groups to work out policies for managing purchased nodes.

The standby queues are available for projects requiring more slots than purchased, or to take advantage of idle nodes when a job would have to wait in the owner queue. Other workgroup nodes will be used, so standby jobs have a time limit, and users are limited to a total number of cores for all of their standby jobs. Generally, users can use 10 nodes for an 8 hour standby job or 40 nodes for a 4 hour standby job.

A spillover queue may be available for the case where a job is submitted to the owner queue, and there are standby jobs consuming needed slots. Instead of waiting, the jobs will be sent to the spillover queue to start on a similar idle node.

The Grid Engine job scheduling system is used to manage and control the computing resources for all jobs submitted to a cluster. This includes load balancing, reconciling requests for memory and processor cores with availability of those resources, suspending and restarting jobs, and managing jobs with different priorities. Grid Engine on Farber is Univa Grid Engine but still referred to as SGE.

In order to schedule any job (interactively or batch) on a cluster, you must set your workgroup to define your cluster group or investing-entity compute nodes.

See Scheduling Jobs and Managing Jobs on the sidebar for general information about getting started with scheduling and managing jobs on a cluster using Grid Engine.

Generally, your runtime environment (path, environment variables, etc.) should be the same as your compile-time environment. Usually, the best way to achieve this is to put the relevant VALET commands in shell scripts. You can reuse common sets of commands by storing them in a shell script file that can be sourced from within other shell script files.

source /etc/profile.d/valet.sh

Grid Engine includes man pages for all of the commands that will be reviewed in this document. When logged-in to a cluster, type

[traine@farber ~]$ man qstat

to learn more about a Grid Engine command (in this case, qstat). Most commands will also respond to the -help command-line option to provide a succinct usage summary:

[traine@farber ~]$ qstat -help
usage: qstat [options]
        [-cb]                             view additional binding specific parameters
        [-ext]                            view additional attributes
           :

This section uses the wiki's documentation conventions.