Spillserver

Spillserver is a software component that manages spill data from in-memory workloads to durable storage when memory pressure occurs. It is used to extend the capacity of applications that operate on large datasets by providing controlled spill and retrieval, while preserving data integrity and ordering where required.

Typically, spillserver comprises a client library that applications call to spill and fetch data, and a spill server process or service that coordinates writes to a storage backend. Supported backends include local filesystems, network-attached storage, and object stores such as S3-compatible services. Data is serialized, optionally compressed, and may be encrypted in transit and at rest. The system implements policies to decide when to spill, how much data to spill, and which data to evict from memory, with options for FIFO or custom eviction strategies and prioritization of hot versus cold data.

Features include fault-tolerant writes with atomic commits, resume capabilities after crashes, multi-tenant isolation, observability through metrics and logs, and pluggable storage backends. Performance considerations focus on minimizing spill and fetch latency, with asynchronous I/O, data caching, and prefetching.

Common use cases are in-memory analytics, streaming systems with large windowed states, and machine learning pipelines that temporarily exceed available RAM. Deployment is typically containerized and cloud-native, with integration into orchestration tools and configuration via environment variables or manifests. While SpillServer-like components are not standardized, they are intended to provide a transparent boundary between memory-bound computation and external storage, enabling more scalable data processing.