ZHAO Xi (赵希)

Research Postgraduate (Started in Sep. 2022, funded by HKPFS)

Computer Science and Engineering

Hong Kong University of Science and Technology

I hold a PhD from the DSF Group in the Department of Computer Science and Engineering at the Hong Kong University of Science and Technology (HKUST), under the supervision of Prof. Xiaofang Zhou. Before my studies at HKUST, I earned my M.Eng from the School of Computer Science and Technology, Huazhong University of Science and Technology (HUST), under the supervision of Prof. Bolong Zheng.

My research focuses on approximate search in vector databases, particularly on algorithms and theories related to high-dimensional vector search. I aim to design high-performance indexes for managing large-scale high-dimensional datasets. Specifically, I investigate locality-sensitive hashing (LSH), vector quantization (VQ), and proximity graphs (APG) for approximate nearest neighbor search (ANNS) and maximum inner product search (MIPS) in high-dimensional vector spaces.

Feel free to contact me if you are interested in my work.

!!! News

I have passed my PhD thesis defense at 9-11AM, Apr 09, 2026. Thanks for the efforts of all committees, including

Prof. Qiming Shao (Chairperson)
Prof. Xiaofang Zhou (Supervisor)
Prof. Raymond Chi-Wing Wong
Prof. Ke Yi
Prof. Sirui Han
Prof. Yunjun Gao (External Examiner)

Educations

PhD in Engineering, Computer Science and Engineering (Funded by HKPFS)

Hong Kong University of Science and Technology, Hong Kong SAR, China (Sept. 2022-Jun. 2026)

Visiting Scholar, School of Computing (Supervised by Prof. Xiaokui Xiao)

National University of Singapore, Singapore (Apr. 2025- Aug. 2025)

Research Assistant, Computer Science and Engineering

Hong Kong University of Science and Technology, Hong Kong SAR, China (Sept. 2021- Sept. 2022)

Master of Engineering, Computer Software and Theory

Huazhong University of Science and Technology, Wuhan, China (Sept. 2018 - Jun. 2021)

Overall GPA: 89.8/100 (3.94/4.00, ranking 1st)

Bachelor of Engineering, Optoelectronic Information Science and Engineering (Honors Class)

Huazhong University of Science and Technology, Wuhan, China (Sept. 2014 - Jun. 2018)

Overall GPA: 88.4/100 (3.84/4.00)

Publications

Xi Zhao, Zhoujin Tian, Kai Huang, Yao Tian, Xiaokui Xiao, Bolong Zheng, Xiaofang Zhou: Enhancing Graph-based Approximate Maximum Inner Product Search via Norm-Adaptive Partitioning. SIGMOD 2026.
Yao Tian, Zhoujin Tian, Xi Zhao, Ruiyuan Zhang, Xiaofang Zhou: GEM: A Native Graph-based Index for Multi-Vector Retrieval. SIGMOD 2026.
Jianheng Tang, Xi Zhao, Lemin Kong, Xiaofang Zhou, Jia Li: Fused Gromov-Wasserstein Alignment for Graph Edit Distance Computation and Beyond. VLDB 2025.
Zhong Yang, Bolong Zheng, Guohui Li, Xi Zhao, Xiaofang Zhou: Universal Set Similarity Search via Multi-Task Representation Learning. ICDE 2025
Haoyu Tang, Ye Liu, Xi Zhao, Xukai Liu, Yanghai Zhang, Kai Zhang, Xiaofang Zhou, Enhong Chen: Learn while Unlearn: An Iterative Unlearning Framework for Generative Language Models. ICDM 2025.
Zhonghan Chen, Ruiyuan Zhang, Xi Zhao, Xiaojun Cheng, Xiaofang Zhou: Exploring the Meaningfulness of Nearest Neighbor Search in High-Dimensional Space. ADC 2024
Xi Zhao, Zhonghan Chen, Kai Huang, Ruiyuan Zhang, Bolong Zheng, Xiaofang Zhou: Efficient Approximate Maximum Inner Product Search over Sparse Vectors. ICDE 2024 [PDF, Technical Report, Slide] [Code]
Kai Huang, Yunqi Li, Qingqing Ye, Yao Tian, Xi Zhao, Yue Cui, Haibo Hu, Xiaofang Zhou: FRESH: Towards Efficient Graph Queries in an Outsourced Graph. ICDE 2024
Jing Zhao, Lei Li, Mengxuan Zhang, Zihan Luo, Xi Zhao, Xiaofang Zhou: A Just-In-Time Framework for Continuous Routing. ICDE 2024
Yao Tian, Ziyang Yue, Ruiyuan Zhang, Xi Zhao, Bolong Zheng, Xiaofang Zhou: Approximate Nearest Neighbor Search in High Dimensional Vector Databases: Current Research and Future Directions. TCDE 2024 (The authors are listed in alphabetical order)[PDF]
Kai Huang, Gaoya Ouyang, Qingqing Ye, Haibo Hu, Bolong Zheng, Xi Zhao, Ruiyuan Zhang, Xiaofang Zhou: LDPGuard: Defenses Against Data Poisoning Attacks to Local Differential Privacy Protocols. TKDE 2024
Kai Huang, Yue Cui, Qingqing Ye, Yan Zhao, Xi Zhao, Yao Tian, Kai Zheng, Haibo Hu, Xiaofang Zhou: TED+: Towards Discovering Top-k Edge-Diversified Patterns in a Graph Database. TKDE 2023
Yao Tian, Xi Zhao, Xiaofang Zhou: DB-LSH 2.0: Locality-Sensitive Hashing With Query-Based Dynamic Bucketing. TKDE 2023
Xi Zhao, Yao Tian, Kai Huang, Bolong Zheng, Xiaofang Zhou: Towards Efficient Index Construction and Approximate Nearest Neighbor Search in High-Dimensional Spaces. PVLDB 2023 [ PDF ] [ Code ]
Xi Zhao, Bolong Zheng, Xiaomeng Yi, Xiaofan Luan, Charles Xie, Xiaofang Zhou, Christian S. Jensen: FARGO: Fast Maximum Inner Product Search via Global Multi-Probing. PVLDB 2023 [PDF] [Code]
Kai Huang, Houdong Liang, Chongchong Yao, Xi Zhao, Yue Cui, Yao Tian, Ruiyuan Zhang, Xiaofang Zhou: VisualNeo: Bridging the Gap between Visual Query Interfaces and Graph Query Engines. PVLDB 2023
Kai Huang, Qingqing Ye, Jing Zhao, Xi Zhao, Haibo Hu, Xiaofang Zhou: VINCENT: Towards Efficient Exploratory Subgraph Search in Graph Databases. PVLDB 2022 (Demo)
Yao Tian, Tingyun Yan, Xi Zhao, Kai Huang, Xiaofang Zhou: A Learned Index for Exact Similarity Search in Metric Spaces. TKDE 2022
Yao Tian, Xi Zhao, Xiaofang Zhou: DB-LSH: Locality-Sensitive Hashing with Query-based Dynamic Bucketing. ICDE 2022 [PDF] [Code]
Bolong Zheng, Xi Zhao, Lianggui Weng, Nguyen Quoc Viet Hung, Hang Liu, Christian S. Jensen: PM-LSH: a fast and accurate in-memory framework for high-dimensional approximate NN and closest pair search. The VLDB Journal 2021
Bolong Zheng, Lianggui Weng, Xi Zhao, Kai Zeng, Xiaofang Zhou, Christian S. Jensen: REPOSE: Distributed Top-k Trajectory Similarity Search with Local Reference Point Tries. ICDE 2021
Zhong Yang, Bolong Zheng, Guohui Li, Xi Zhao, Xiaofang Zhou, Christian S. Jensen: Adaptive Top-k Overlap Set Similarity Joins. ICDE 2020
Bolong Zheng, Xi Zhao, Lianggui Weng, Nguyen Quoc Viet Hung, Hang Liu, Christian S. Jensen: PM-LSH: A Fast and Accurate LSH Framework for High-Dimensional Approximate NN Search. PVLDB 2020 (one of the best PVLDB 2020 papers) [PDF] [Code]

Professional Services and Teaching

Teaching Assistant

COMP2711H. Honors Discrete Mathematical Tools for Computer Science (Honored Course), HKUST, Fall 2025
COMP1029C. C Bridging Course, HKUST, Fall 2024
COMP1029C. C Bridging Course, HKUST, Spring 2024
COMP3711. Design and Analysis of Algorithms, HKUST, Spring 2023

Reviewer

ICDE 2024, CCF-A Conference.
TKDE(2025), CCF-A Journal.
JSA(2026), CCF-B Journal.

Others

I am the volunteered server admin for managing the DSF's 15 Ubuntu servers with others, including GPU servers(40* Nvidia A100, 16* Nvidia 4090), CPU servers and storage servers.

Selected Honors and Awards

HKUST Overseas Research Award, 2025
Hong Kong PhD Fellowship, HKUST, 2022
HKUST RedBird PhD Scholarship, HKUST, 2022
Outstanding Graduates, HUST, 2021
One of the best PVLDB 2020 papers, HUST, 2020
National Scholarship for Graduates, HUST, 2020
Outstanding Undergraduates, HUST, 2018
National Encouragement Scholarship, HUST, 2017
The 1st Prize in Mathematics Competition of Chinese College Students, HUST, 2016

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