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I am broadly interested in database theory and its applications to practical database systems, such as massively parallel query processing, dynamic query processing, oblivious query processing, and machine learning in query optimization. I am part of the Data System Group and affiliated with Algorithms & Complexity Group at the Univeristy of Waterloo.
I am looking for PhD and MMath students. Please send me an email and mention me as a potential advisor in your application.
Preprints
Xiao Hu. “Output-Optimal Algorithms for Join-Aggregate Queries.” [arxiv]
Mahmoud Abo-Khamis, Xiao Hu and Dan Suciu. “Fast Matrix Multiplication meets the Subdmodular Width.” [arxiv]
Publications
Pankaj K. Agarwal, Aryan Esmailpour, Xiao Hu, Stavros Sintos, and Jun Yang. “Computing A Well-Representative Summary of Conjunctive Query Results.” ACM Symposium on Principles of Database Systems (PODS), June 2025. [pdf]
Xiao Hu and Zhiang Wu. “Oblivious Optimal Algorithms for Multi-way Joins.” International Conference on Database Theory (ICDT), March 2025.
Xiao Hu. “Fast Matrix Multiplication for Query Processing”, ACM Symposium on Principles of Database Systems (PODS), June 2024. [pdf]
Xiao Hu and Paraschos Koutris. “Topology-aware Parallel Joins”, ACM Symposium on Principles of Database Systems (PODS), June 2024. [pdf] (Distinguished Paper Award) (invited to TODS)
Pankaj K. Agarwal, Xiao Hu, Stavros Sintos, and Jun Yang. “Reporting Durable Patterns in Temporal Graphs Efficiently”, ACM Symposium on Principles of Database Systems (PODS), June 2024. [pdf]
Binyang Dai, Xiao Hu and Ke Yi. “Reservoir Sampling over Joins”, ACM SIGMOD International Conference on Management of Data (SIGMOD), June 2024. [pdf] [arxiv] (Best Paper Award Honorable Mention) (invited to TODS)
Zichen Zhu, Xiao Hu, Manos Athanassoulis. “NOCAP: Near-Optimal Correlation-Aware Partitioning Joins”, ACM SIGMOD International Conference on Management of Data (SIGMOD), June 2024. [pdf][arxiv]
Xiao Hu and Stavros Sintos. “Finding Smallest Witness for Conjunctive Query”, International Conference on Database Theory (ICDT), March 2024. [pdf] [arxiv] (Best Paper Award) (invited to TODS)
Xiao Hu and Yufei Tao. “Parallel Acyclic Joins: Optimal Algorithms and Cyclicity Separation”, Journal of the ACM (JACM), Volume 71, Issue 1, Article No.: 6, Pages 1 - 44, February 2024. [pdf]
Badih Ghazi, Xiao Hu, Ravi Kumar and Pasin Manurangsi. “On Differentially Private Sampling from Gaussian and Product Distributions”, Thirty-seventh Conference on Neural Information Processing Systems (NeurIPS), December 2023. [pdf][arxiv]
Qichen Wang, Xiao Hu, Binyang Dai and Ke Yi. “Change Propagations Without Joins”, International Conference on Very Large Data Bases (VLDB), August 2023. [pdf]
Shaleen Deep, Xiao Hu and Paraschos Koutris. “General Space-Time Tradeoffs via Relational Queries.” Algorithms and Data Structures Symposium (WADS), July 2023. [arxiv]
Badih Ghazi, Xiao Hu, Ravi Kumar and Pasin Manurangsi. “Differentially Private Data Release over Multiple Tables.” ACM Symposium on Principles of Database Systems (PODS), June 2023. [pdf]
Xiao Hu and Qichen Wang. “Computing the Difference of Conjunctive Queries Efficiently”, ACM SIGMOD International Conference on Management of Data (SIGMOD), June 2023. [pdf]
Shaleen Deep, Xiao Hu and Paraschos Koutris. “Ranked Enumeration of Join Queries with Projections.” International Conference on Very Large Data Bases (VLDB), September 2022. [pdf]
Xiao Hu, Yuxi Liu, Haibo Xiu, Pankaj K. Agarwal, Debmalya Panigrahi, Sudeepa Roy, and Jun Yang. “Selectivity Functions of Range Queries are Learnable.” ACM SIGMOD International Conference on Management of Data (SIGMOD), June 2022. [pdf]
Xiao Hu, Stavros Sintos, Junyang Gao, Pankaj K. Agarwal, and Jun Yang. “Computing Complex Temporal Join Queries Efficiently.” ACM SIGMOD International Conference on Management of Data (SIGMOD), June 2022. [pdf]
Xiao Hu, Shouzhuo Sun, Shweta Patwa, Debmalya Panigrahi and Sudeepa Roy. “Aggregated Deletion Propagation for Counting Conjunctive Query Answers.” International Conference on Very Large Data Bases (VLDB), August 2021. [pdf][arxiv]
Pankaj K. Agarwal, Xiao Hu, Stavros Sintos, and Jun Yang. “Dynamic Enumeration of Similarity Joins.” International Colloquium on Automata, Languages and Programming (ICALP), July 2021. [pdf][arxiv]
Xiao Hu. “Cover or Pack: New Upper and Lower Bounds for Massively Parallel Joins.” ACM Symposium on Principles of Database Systems (PODS), June 2021. [pdf]
Xiao Hu, Paraschos Koutris and Spyros Blanas. “Algorithms for a Topology-aware Massively Parallel Computation Model.” ACM Symposium on Principles of Database Systems (PODS), June 2021. [pdf][arXiv]
Shaleen Deep, Xiao Hu and Paraschos Koutris. “Enumeration Algorithms for Conjunctive Queries with Projection.” International Conference on Database Theory (ICDT), March 2021. [pdf][arxiv] (invited to LMCS)
Xiao Hu and Ke Yi. “Massively Parallel Join Algorithms.” SIGMOD Record, 49(3), September 2020 (invited). [pdf]
Xiao Hu and Ke Yi. “Parallel Algorithms for Sparse Matrix Multiplication and Join-Aggregate Queries.” ACM Symposium on Principles of Database Systems (PODS), June 2020. [pdf]
Shaleen Deep, Xiao Hu and Paraschos Koutris. “Fast Join Project Query Evaluation using Matrix Multiplication.” ACM SIGMOD International Conference on Management of Data (SIGMOD), June 2020. [pdf][arXiv]
Xiao Hu, Ke Yi, and Yufei Tao. “Output-optimal Massively Parallel Algorithms for Similarity Joins.” ACM Transactions on Database Systems (TODS), 44(2):6, April 2019 (invited). [pdf]
Xiao Hu and Ke Yi. “Instance and Output Optimal Parallel Algorithms for Acyclic Joins.” ACM Symposium on Principles of Database Systems (PODS), June 2019. [pdf][arXiv]
Zhuoyue Zhao, Robert Christensen, Feifei Li, Xiao Hu, and Ke Yi. “Random Sampling over Joins Revisited.” ACM SIGMOD International Conference on Management of Data (SIGMOD), June 2018. [pdf]
Xiao Hu, Yufei Tao, and Ke Yi. “Output-optimal Parallel Algorithms for Similarity Joins.” ACM Symposium on Principles of Database Systems (PODS), May 2017. [pdf] (invited to TODS)
Xiao Hu and Ke Yi. “Towards a Worst-Case I/O-Optimal Algorithm for Acyclic Joins.” ACM Symposium on Principles of Database Systems (PODS), June 2016. [pdf]
Students
Zhiang Wu (PhD, since 2023 Fall)
Boyi Li (MMath, since 2024 Winter)
Jatin Mehta (Undergraduate, CS URA 2024 Fall)
Teaching
Instructor: University of Waterloo, CS 348 Introduction to Database Systems, Spring 2025.
Instructor: Univesity of Waterloo, CS 848 Advanced Topics in Databases (online), Spring 2024.
Co-Instructor: Duke Univesity, CompSci 316 Introduction to Database Systems, Fall 2021.
Awards & Grants
PODS 2024 Distinguished Paper Award
Overseas Research Award, HKUST
SENG Top RPg Award, HKUST
Services
Program Committee: SIGMOD 2026, SIGMOD 2025, VLDB 2025, ICDT 2025, PODS 2024, VLDB 2024, PODS 2023, SIGMOD 2023, NeurIPS 2022, PODS 2022, ICDT 2022, ICDE 2022, SIGMOD 2021 (Demonstration Track), ICDE 2021 (Demonstration Track).
Reviewer: TODS, TKDE, LMCS, SODA, SoCG.
Committee: Women in Computer Science 2024-2025, University of Waterloo.
Committee: ICDT Test-of-Time Award 2025.
Co-chair: VLDB 2023 PhD Workshop.
Bio
I was a Research Fellow in Simons Institute for the Theory of Computing related to the program Logic and Algorithms in Database Theory and AI in Fall 2023. I was a Visiting Faculty Scholar in the Discrete Algorithm Group at Google Research and worked with Pasin Manurangsi, Badih Ghazi and Ravi Kumar. Before that, I was a postdoctoral associate within the Department of Computer Science at Duke University, co-supervised by Prof. Pankaj Agarwal and Prof. Jun Yang. I received my Ph.D. from the Department of Computer Science and Technology at HKUST in August 2019, under the supervision of Prof. Ke Yi. From Feb 2019 to May 2019, I was a visiting scholar in the Department of Computer Sciences at the University of Wisconsin Madison and worked with Paris Koutris. Before that, I received my Bachelor's Degree in Engineering from the School of Software at Tsinghua University in 2014.