Interactive or batch
You can run computations interactively or in batch.
Interactive processing is the simplest way to work on a system. You log in, run commands which execute immediately, and log off when you've finished. You can use either the command line or a graphical environment.
Interactive jobs run directly on the limited number of login nodes (servers) on each cluster. DiAL3 has two login nodes. Although user login sessions are spread across these nodes, interactive processes will be competing with each other.
When should you use interactive processing?
- Short tasks
- Tasks that require frequent user interaction
- Graphically intensive tasks
The design of DIaL3 is strongly biased towards batch jobs. It has 200 compute nodes and only two login nodes. Therefore interactive processes on DIaL3 shouldn't take more than a few minutes of CPU time.
Although there are no hard limits (in terms of usage time) applied on the login nodes, you should never use it for heavy processing. Furthermore, should the administrators be alerted to heavy processing on the login nodes, those processes are likely to be killed with no warning in order to ensure the login nodes remain responsive for everyone.
What if you need to run longer processes interactively?
You can submit jobs to the scheduler for interactive running. These jobs provide a login to one of the compute nodes with the requested resources dedicated to you. These jobs support X-forwarding so graphical applications will work as normal. For more information, see Interactive jobs.
What is batch processing?
Batch processing is more complex because work has to carefully planned and able to run without user interaction. Batch jobs are submitted to a job scheduler and run on the first available compute node(s). Once submitted, you can log off and wait for the jobs to complete, with the option to be sent an email when this has happened. Although batch jobs may have to wait in a queue before running, they are then given a dedicated set of resources to ensure that they complete as quickly as possible.
When should you use batch processing?
- Longer running processes
- Parallel processes
- Running large numbers of short jobs simultaneously
- Tasks that can be left running for a significant amount of time without any interaction