# SaGe: Web Preemption for Public SPARQL Query Services

## TL;DR

SaGe introduces a novel Web preemption model for SPARQL query services, enabling suspension and resumption of queries to improve responsiveness and stability in public data servers.

## Contribution

It proposes SaGe, the first SPARQL engine with Web preemption, allowing query suspension and resumption with minimal overhead, enhancing public query service performance.

## Key findings

- SaGe significantly reduces total query execution time.
- SaGe outperforms existing approaches in first result latency.
- Preemption cost in SaGe is negligible compared to the time quantum.

## Abstract

To provide stable and responsive public SPARQL query services, data providers enforce quotas on server usage. Queries which exceed these quotas are interrupted and deliver partial results. Such interruption is not an issue if it is possible to resume queries execution afterward. Unfortunately, there is no preemption model for the Web that allows for suspending and resuming SPARQL queries. In this paper, we propose SaGe: a SPARQL query engine based on Web preemption. SaGe allows SPARQL queries to be suspended by the Web server after a fixed time quantum and resumed upon client request. Web preemption is tractable only if its cost in time is negligible compared to the time quantum. The challenge is to support the full SPARQL query language while keeping the cost of preemption negligible. Experimental results demonstrate that SaGe outperforms existing SPARQL query processing approaches by several orders of magnitude in term of the average total query execution time and the time for first results.