spark-sched-sim
An Apache Spark job scheduling simulator, implemented as a Gymnasium environment.
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| Two Gantt charts comparing the behavior of different job scheduling algorithms. In these experiments, 50 jobs are identified by unique colors and processed in parallel by 10 identical executors (stacked vertically). Decima achieves better resource packing and lower average job completion time than Spark's fair scheduler. |
What is job scheduling in Spark?
- A Spark application is a long-running program within the cluster that submits jobs to be processed by its share of the cluster's resources. Each job encodes a directed acyclic graph (DAG) of stages that depend on each other, where a dependency $A\to B$ means that stage $A$ must finish executing before stage $B$ can begin. Each stage consists of many identical tasks which are units of work that operate over different shards of data. Tasks are processed by executors, which are JVM's running on the cluster's worker nodes.
- Scheduling jobs means designating which tasks runs on which executors at each time.
- For more backround on Spark, see this article.
Why this simulator?
- Job scheduling is important, because a smarter scheduling algorithm can result in faster job turnaround time.
- This simulator allows researchers to test scheduling heuristics and train neural schedulers using reinforcement learning.
This repository is a PyTorch Geometric implementaion of the Decima codebase, adhering to the Gymnasium interface. It also includes enhancements to the reinforcement learning algorithm and model design, along with a basic PyGame renderer that generates the above charts in real time.
Enhancements include:
- Continuously discounted returns, improving training speed
- Proximal Polixy Optimization (PPO), improving training speed and stability
- A restricted action space, encouraging a fairer policy to be learned
- Multiple different job sequences experienced per training iteration, reducing variance in the policy gradient (PG) estimate
- No learning curriculum, improving training speed
After cloning this repo, please run pip install -r requirements.txt to install the project's dependencies.
To start out, try running examples via examples.py --sched [fair|decima]. To train Decima from scratch, modify the provided config file config/decima_tpch.yaml as needed, then provide the config to train.py -f CFG_FILE.