IIU: Specialized architecture for inverted index search

Abstract

Inverted index serves as a fundamental data structure for efficient search across various applications such as full-text search engine, document analytics, and other information retrieval systems. The storage requirement and query load for these structures have been growing at a rapid rate. Thus, an ideal indexing system should maintain a small index size with a low query processing time. Previous works have mainly focused on using CPUs and GPUs to exploit query parallelism while utilizing state-of-the-art compression schemes to fit the index in memory. However, scaling parallelism to maximally utilize memory bandwidth on these architectures is still challenging. In this work, we present IIU1, a novel inverted index processing unit, to optimize the query performance while maintaining a low memory overhead for index storage. To this end, we co-design the indexing scheme and hardware accelerator so that the accelerator can process highly compressed inverted index at high throughput. In addition, IIU provides flexible interconnects between modules to take advantage of both intra- and inter-query parallelism. Our evaluation using a cycle-level simulator demonstrates that IIU provides an average of 13.8× query latency reduction and 5.4× throughput improvement across different query types while reducing the average energy consumption by 18.6×, compared to Apache Lucene, a production-grade full-text search framework.