Consistency-based service level agreements for cloud storage

TLDR

Choosing a cloud storage system and operations requires trade‑offs between consistency, availability, and performance, and applications may be locked into suboptimal choices as conditions change. Pileus is a replicated key‑value store that lets applications specify consistency and latency priorities through consistency‑based service level agreements. It dynamically selects servers to meet declared SLAs, allowing developers to request strong, eventual, or intermediate guarantees such as read‑my‑writes. Tests on a global geo‑replicated test bed show that Pileus adapts to client‑server latency variations, delivering service that matches or surpasses the best static consistency and server‑selection schemes.

Abstract

Choosing a cloud storage system and specific operations for reading and writing data requires developers to make decisions that trade off consistency for availability and performance. Applications may be locked into a choice that is not ideal for all clients and changing conditions. Pileus is a replicated key-value store that allows applications to declare their consistency and latency priorities via consistency-based service level agreements (SLAs). It dynamically selects which servers to access in order to deliver the best service given the current configuration and system conditions. In application-specific SLAs, developers can request both strong and eventual consistency as well as intermediate guarantees such as read-my-writes. Evaluations running on a worldwide test bed with geo-replicated data show that the system adapts to varying client-server latencies to provide service that matches or exceeds the best static consistency choice and server selection scheme.