Backfilling

What is backfilling?

Backfilling is a technique used in high-performance computing (HPC) to maximize the utilization of server clusters. This method allows a job with a lower priority to be started before a job with a higher priority without delaying the execution of the job with a higher priority.

Functionality

The Principle of backfilling is based on the optimal use of free capacities in a cluster. If not all resources are required for a prioritized job, remaining capacities can be used to process smaller jobs in the background. This effectively fills "gaps" in the allocation plan, resulting in better throughput.

Advantages and requirements

So that a job from Backfilling If you want to benefit from a job, its planned duration must be significantly shorter than that of the jobs already running. The exact duration must be specified in advance. A practical example of this is the setting of the runtime in Slurm: A line like #SBATCH --time=2-12:00:00 specifies a maximum runtime of 2 days and 12 hours. Shorter times increase the chance that the job will be inserted into a free gap. If the job reaches the specified time limit, it is automatically terminated by the batch system.

Mechanism of the backfill

The Mechanism of the backfill allows jobs with a lower priority to start before those with a higher priority, without delaying the execution of the priority jobs. The aim is to maximize the throughput in a cluster by filling the "gaps" in the allocation plan.

Specific requirements

For the effective use of Backfilling it is important that the runtime of the low-priority job is considerably shorter than the standard maximum time. This planned shorter runtime must be specified when the job is submitted. This ensures that the job is completed before a machine that is required for a prioritized task becomes free. This ensures that the Backfilling-strategy works efficiently and without delays for important work.

Example for illustration

An illustrative example: If job A is already running and job B has a higher priority than job C, job C can still start before job B. The prerequisite is that job C has a shorter runtime than job A. This means that the higher priority of job B is not affected, as job A is not blocked and the free capacity is used efficiently.

How backfilling works

The Functionality of Backfilling aims to maximize the utilization of server capacities in an HPC cluster. Schedulers analyze the available resources and identify gaps that can be efficiently filled by smaller jobs. This ensures that no capacities remain unused and that the entire cluster is optimally utilized.

Step-by-step process

The process begins with the scheduler determining the maximum available resources for prioritized jobs. It then checks whether smaller, less prioritized jobs can use these remaining resources without affecting the execution of the important jobs. Based on this analysis, a sequence of jobs is created that ensures that all capacities are used in the best possible way.

This method prevents resources from lying idle by scheduling tasks in such a way that even less urgent jobs can be processed immediately. Schedulers play a central role here, as they continuously monitor the utilization of the cluster and adjust accordingly.

Maximizing efficiency

An essential Advantage of backfilling is the avoidance of idle time within the server environment. By placing short-term jobs that can be completed quickly in the available gaps, the overall job throughput of the cluster is increased. This leads to improved efficiency and shorter waiting times for all incoming tasks. Depending on the size and scope of the cluster, up to 100 jobs can be executed simultaneously using this strategy.

Significance for IT development

The Importance of backfilling for IT development is immense, especially for companies outside the IT sector. These companies need to focus on their core competencies and develop innovative products and services at the same time. In this context, IT may take a back seat, but it remains indispensable. Backfilling enables these companies to use their IT resources efficiently and thus react more quickly to market requirements.

Advantages for IT service providers

For IT service providers, the range of technologies such as Backfilling represents a clear competitive advantage. Non-IT companies benefit from the efficiency and ability to make optimal use of IT resources without having to set up large internal IT departments. In this way, IT service providers can offer sophisticated projects, such as application managed services, and thus meet the needs of these companies.

Through the use of Backfilling IT service providers can help their customers to shorten development cycles and complete innovation projects more quickly. This is particularly important in industries with rapid change and intense competition.

Scalable solutions

Another important aspect is scalability. Backfilling enables IT resources to be flexibly adapted to different workloads. This makes it easier for companies to work efficiently even at peak times and complete their projects on time. This not only increases productivity, but also customer satisfaction.

Through the efficient use of Backfilling IT service providers can offer their customers a clear cost advantage, as unused resources can be avoided and operating costs can be reduced accordingly. This makes Backfilling an indispensable tool in the modern IT landscape.

Setting the runtime in Slurm

The Setting the runtime in Slurm is a key factor when it comes to planning jobs efficiently and optimizing the Backfilling to use. Slurm, a popular open source job scheduler system for Linux clusters, allows users to precisely specify the maximum runtime of their jobs. This is achieved by specifying the time in the job's configuration file, for example with the line #SBATCH --time=2-12:00:00. This line sets an upper limit for the job runtime of 2 days and 12 hours.

Increasing the chances of backfilling

By specifying shorter runtimes, users can increase the likelihood that their jobs will be recognized by the Backfilling benefit. For example, if a user specifies a significantly shorter runtime for a job, the scheduler can insert this job into an existing gap while waiting for full resources to become available for prioritized jobs. This leads to a more effective use of cluster resources and reduces the waiting times for all submitted jobs.

Another important point is that when the job reaches the specified time limit, it is automatically terminated by the batch system. This helps to make optimum use of resources and ensure that no jobs remain in the queue indefinitely. Further information and detailed instructions on setting the runtime can be found in the sbatch manual.

Practical applications

In practice, this enables more flexible and efficient management of resources within a cluster. Especially in large HPC environments, where many jobs run simultaneously, the precise setting of runtimes can make a significant difference to the overall utilization and efficiency of the system. This helps to optimize workflows and achieve better results in less time.

In summary, the correct setting of the runtime in Slurm is an essential tool for realizing the potential of Backfilling and maximize the efficiency of HPC systems.

Role of the scheduler in backfilling

The Role of the scheduler in the Backfilling is central to the efficient use of cluster resources. Schedulers are programs that decide which jobs are to be executed at which time on which part of a cluster. In the context of the Backfilling schedulers continuously analyze the available resources and identify free capacity that can be filled by lower-priority jobs without delaying the execution of higher-priority jobs.

Important scheduler functions

A crucial aspect of schedulers is their ability to create a sequence of jobs that ensures the best possible utilization of resources. In doing so, they take into account both the priority of the jobs and their runtimes. Schedulers are particularly designed to avoid undesirable gaps in resource utilization by using more flexible and short-lived jobs.

A practical example: If a scheduler recognizes that a prioritized job A is taking up a large amount of resources and will be completed shortly, it can have a lower-priority job B started in the meantime, using only a small portion of the remaining resources. As soon as Job A is completed, the scheduler can allocate the freed-up resources to another prioritized job without Job B affecting the higher priority.

Enhanced scheduling techniques

Not all schedulers inherently support complex methods such as Backfilling. In such cases, additional modules or updates can be installed to integrate these functionalities. Another advanced function that is often used together with Backfilling is the method of the FairShare. This ensures that resources are distributed fairly over longer periods of time and that all user groups are considered equally.

In summary, schedulers are essential for the implementation and success of backfilling. They play a key role in continuously monitoring and adjusting resource allocation in a cluster to maximize both efficiency and fairness. By integrating techniques such as Backfilling schedulers make a decisive contribution to the optimal use of resources and thus to the performance of large data centers.