Fast Query Decomposition for Batch Shortest Path Processing in Road Networks

Shortest path query is a fundamental operation in various location-based services (LBS) and most of them process queries on the server-side. As the business expands, scalability becomes a severe issue. Instead of simply deploying more servers to cope with the quickly increasing query number, batch shortest path algorithms have been proposed recently to answer a set of queries together using shareable computation. Besides, they can also work in a highly dynamic environment as no index is needed. However, the existing batch algorithms either assume the batch queries are finely decomposed or just process them without differentiation, resulting in poor query efficiency. In this paper, we aim to improve the performance of batch shortest path algorithms by revisiting the problem of query clustering. Specifically, we first propose three query decomposition methods to cluster queries: Zigzag that considers the 1-N shared computation; Search-Space Estimation that further incorporates search space estimation; and Co-Clustering that considers the source and target's spatial locality. After that, we propose two batch algorithms that take advantage of the previously decomposed query sets for efficient query answering: Local Cache that improves the existing Global Cache with higher cache hit ratio, and R2R that finds a set of approximate shortest paths from one region to another with bounded error. Experiments on a large real-world query sets verify the effectiveness and efficiency of our decomposition methods compared with the state-of-the-art batch algorithms.