How the Grid Engine System Allocates Resources

As shown in the previous section, knowing how grid engine software processes resource requests and allocates resources is important. The schematic view of grid engine software's resource allocation algorithm is as follows.

1. Read in and parse all default request files. See Default Request Files for details.

2. Process the script file for embedded options. See Active Comments for details.

3. Read all script-embedding options when the job is submitted, regardless of their position in the script file.

4. Read and parse all requests from the command line.

As soon as all qsub requests are collected, hard and soft requests are processed separately, the hard requests first. The requests are evaluated, according to the following order of precedence:

1. From left to right of the script or default request file

2. From top to bottom of the script or default request file

3. From left to right of the command line

In other words, you can use the command line to override the embedded flags.

The resources requested as hard are allocated. If a request is not valid, the submission is rejected. If one or more requests cannot be met at submit time, the job is spooled and rescheduled to be run at a later time. A request might not be met, for example, if a requested queue is busy. If all hard requests can be met, the requests are allocated and the job can be run.

The resources requested as soft are checked. The job can run even if some or all of these requests cannot be met. If multiple queues that meet the hard requests provide parts of the soft resources list, the grid engine software selects the queues that offer the most soft requests.

The job is started and covers the allocated resources.

You might want to gather experience of how argument list options and embedded options or hard and soft requests influence each other. You can experiment with small test script files that execute UNIX commands such as hostname or date.