Approximate Nearest Neighbor Search (ANNS) plays an important role in the search and recommendation of objects represented with high-dimensional vectors. For objects that are associated with tags such as the origin location, color, and type, it is common to perform ANNS with tag constraints, i.e., conduct search on objects that carry the query tags. We call such search Tag-Filtered Approximate Nearest Neighbor Search (TFANNS). The state-of-the-art TFANNS method Filtered-DiskANN is a graph-based method which suffers from a low recall for queries with low-to-medium frequent tags. Pre-filtering on these tags could boost the recall but lead to a large memory footprint. To address this issue, we propose three strategies in constructing a graph that strikes a balance between the performance and memory footprint; note that we are the first work on tag-frequency-aware graph-based indexing for TFANNS. Our extensive experiments show the superiority of our proposed methods over existing baselines: under$\geq 0.9$recall, our QPS is up to 13 times that of the best baseline.

Effective vector representation models, e.g., word2vec and node2vec, embed real-world objects such as images and documents in high dimensional vector space. In the meanwhile, the objects are often associated with attributes such as timestamps and prices. Many scenarios need to jointly query the vector representations of the objects together with their attributes. These queries can be formalized as range-filtering approximate nearest neighbor search (ANNS) queries. Specifically, given a collection of data vectors, each associated with an attribute value whose domain has a total order. The range-filtering ANNS consists of a query range and a query vector. It finds the approximate nearest neighbors of the query vector among all the data vectors whose attribute values fall in the query range. Existing approaches suffer from a rapidly degrading query performance when the query range width shifts. The query performance can be optimized by a solution that builds an ANNS index for every possible query range; however, the index time and index size become prohibitive -- the number of query ranges is quadratic to the number n of data vectors. To overcome these challenges, for the query range contains all attribute values smaller than a user-provided threshold, we design a structure called the segment graph whose index time and size are the same as a single ANNS index, yet can losslessly compress the n ANNS indexes, reducing the indexing cost by a factor of Ω(n). To handle general range queries, we propose a 2D segment graph with average-case index size O(n log n) to compress n segment graphs, breaking the quadratic barrier. Extensive experiments conducted on real-world datasets show that our proposed structures outperformed existing methods significantly; our index also exhibits superior scalability.

Alibaba relies on its robust database infrastructure to facilitate realtime data access and ensure business continuity despite regional disruptions. To address these operational imperatives, Alibaba developed the Data Transmission Service (DTS), which has become critical for internal applications and public cloud services alike. This paper presents a comprehensive study of the architectural innovations, resource scheduling mechanisms, and performance optimization strategies that have been implemented within DTS to tackle the significant challenges of cross-network, heterogeneous data transmission in a cost-effective manner. We explore the novel Any-to-Any (A2A) architecture, which simplifies the complexity of data paths between diverse databases and mitigates network connectivity issues, thereby significantly reducing development overhead. Additionally, we examine a dynamic network bandwidth scheduling algorithm that effectively maintains Service-Level Objectives (SLOs), complemented by a serverless mechanism that ensures efficient resource utilization. Furthermore, DTS utilizes advanced strategies such as transaction dependency tracking, hot data consolidation, and batching to enhance synchronization performance and efficiency. DTS has distilled the lessons learned from years of serving our customer base and currently supports nearly 1 million public cloud instances annually. Our evaluation results show that DTS can effectively and efficiently handle real-time data transmission in both experimental and production environments.

Given a collection of vectors, the approximate K-nearest-neighbor graph (KGraph for short) connects every vector to its approximate K-nearest-neighbors (KNN for short). KGraph plays an important role in high dimensional data visualization, semantic search, manifold learning, and machine learning. The vectors are typically vector representations of real-world objects (e.g., images and documents), which often come with a few structured attributes, such as times-tamps and locations. In this paper, we study the all-range approximate K-nearest-neighbor graph (ARKGraph) problem. Specifically, given a collection of vectors, each associated with a numerical search key (e.g., a timestamp), we aim to build an index that takes a search key range as the query and returns the KGraph of vectors whose search keys are within the query range. ARKGraph can facilitate interactive high dimensional data visualization, data mining, etc. A key challenge of this problem is the huge index size. This is because, given n vectors, a brute-force index stores a KGraph for every search key range, which results in O (K n 3 ) index size as there are O ( n 2 ) search key ranges and each KGraph takes O (K n ) space. We observe that the KNN of a vector in nearby ranges are often the same, which can be grouped together to save space. Based on this observation, we propose a series of novel techniques that reduce the index size significantly to just O (K n log n ) in the average case. Furthermore, we develop an efficient indexing algorithm that constructs the optimized ARKGraph index directly without exhaustively calculating the distance between every pair of vectors. To process a query, for each vector in the query range, we only need O (log log n + K log K) to restore its KNN in the query range from the optimized ARKGraph index. We conducted extensive experiments on real-world datasets. Experimental results show that our optimized ARKGraph index achieved a small index size, low query latency, and good scalability. Specifically, our approach was 1000x faster than the baseline method that builds a KGraph for all the vectors in the query range on-the-fly.

In this paper, we study the near-duplicate text alignment search problem, which, given a collection of source (data) documents and a suspicious (query) document, finds all the near-duplicate passage pairs between the suspicious document and every source document. It finds applications in plagiarism detection. Specifically, the first two steps in plagiarism detection are source retrieval and text alignment. Source retrieval finds candidate source documents in a corpus that share content with the suspicious document while text alignment finds all the similar passage pairs between the suspicious document and every candidate source document. This problem is computation-intensive, especially for long documents. This is because there are O(n2m2) passage pairs between a single source document with n words and a suspicious document with m words, not to mention the large number of source documents in a corpus. Due to the high computation cost, existing solutions primarily rely on heuristic rules, such as the "seeding-extension-filtering" pipeline, and involve many hard-to-tune hyper-parameters. To address these issues, a recent work ALLIGN leverages the min-wise hash sketch for the text alignment problem. However, ALLIGN only works for two documents and leaves the source retrieval problem unattended. In this paper, we propose to leverage the bottom-k sketch (a.k.a. conditional random sampling) to estimate the similarity of two passages. We observe that many nearby passages in a document would share the same bottom-k sketch. Thus we propose to group all the passages in a document by their sketches. We prove that all the O(n2) passages can be partitioned into O(nk) groups in a document with n words and develop an algorithm to generate these groups in O(nlogn+nk) time. Then, to address the source retrieval problem, we only need to find groups of passages with "similar" bottom-k sketches. Every passage pair in two groups with "similar" sketches are near-duplicates. Experimental results on real-world datasets show that our techniques are highly efficient.

Program synthesis (a.k.a. programming-by-example, PBE) has been deployed in several widely-used commercial products, such as Microsoft Excel, Power BI, and Google Spreadsheet, due to its effectiveness and user-friendliness. It takes a few user-provided positive and negative examples as input and produces a program that is consistent with all the examples, which helps end-users wrangle messy texts without writing any code. In this paper, we focus on two text wrangling tasks, string filtering and transformation. Existing PBE systems for string filtering do not scale well with negative examples. This is because they first explicitly synthesize all the consistent programs and then greedily search a good one in them. However, when there are negative examples, it could take an exponential time and space to synthesize all the exponential number of consistent programs. In contrast, we propose to synthesize all the programs consistent with the positive examples first and then lazily determine whether a program is also consistent with all the negative examples on demand in the search step. For this purpose, we develop a dynamic programming algorithm to search the optimal consistent program. Many programs are never explored during dynamic programming as they are dominated by other better consistent programs. As for string transformation, existing PBE systems do not even support negative examples. Our approach naturally extends to string transformation. Experimental results show that our methods significantly outperformed the state-of-the-art string filtering and transformation approaches and achieved better scalability.

Understanding representativeness in cellular web logs at city scale is essential for web applications. Most of the existing work on cellular web analyses or applications is built upon data from a single network in a city, which may not be representative of the overall usage patterns since multiple cellular networks coexist in most cities in the world. In this paper, we conduct the first comprehensive investigation of multiple cellular networks in a city with a 100% user penetration rate. We study web usage pattern (e.g., internet access services) correlation and difference between diverse cellular networks in terms of spatial and temporal dimensions to quantify the representativeness of web usage from a single network in usage patterns of all users in the same city. Moreover, relying on three external datasets, we study the correlation between the representativeness and contextual factors (e.g., Point-of-Interest, population, and mobility) to explain the potential causalities for the representativeness difference. We found that contextual diversity is a key reason for representativeness difference, and representativeness has a significant impact on the performance of real-world applications. Based on the analysis results, we further design a correction model to address the bias of single cellphone networks and improve representativeness by 45.8%.