The surge in large language models (LLMs) has fundamentally reshaped the landscape of GPU usage patterns, creating an urgent need for more efficient management strategies. While cloud providers employ spot instances to reduce costs for low-priority (LP) tasks, existing schedulers still grapple with high eviction rates and lengthy queuing times. To address these limitations, we present GFS, a novel preemptive scheduling framework that enhances service-level objective (SLO) compliance for high-priority (HP) tasks while minimizing preemptions to LP tasks. Firstly, GFS utilizes a lightweight forecasting model that predicts GPU demand among different tenants, enabling proactive resource management. Secondly, GFS employs a dynamic allocation mechanism to adjust the spot quota for LP tasks with guaranteed durations. Lastly, GFS incorporates a preemptive scheduling policy that prioritizes HP tasks while minimizing the impact on LP tasks. We demonstrate the effectiveness of GFS through both real-world implementation and simulations. The results show that GFS reduces eviction rates by 33.0%, and cuts queuing delays by 44.1% for LP tasks. Furthermore, GFS enhances the GPU allocation rate by up to 22.8% in real production clusters. In a production cluster of more than 10,000 GPUs, GFS yields roughly $459,715 in monthly benefits.

Recovering trajectories of all moving vehicles from urban-scale cameras is an attractive but challenging topic for massive video data management. Existing solutions frame it as an iterative image clustering problem. The snapshots from the same vehicle are grouped within a cluster, which is further refined according to the spatial-temporal attributes. However, these approaches exhibit expensive iterative clustering overhead and ineffective exploitation of spatial-temporal clues. Moreover, they are designed for batch processing, facing performance degradation when handling newly collected surveillance data. In this paper, we propose a novel joint representation clustering framework, which recovers trajectories from vehicle snapshots in an efficient and accurate fashion and is inherently suited for processing video streaming data. Technically, spatial-temporal features are explicitly extracted to construct the joint representation, eliminating the need for iterative refinement, which significantly reduces computational overhead. Furthermore, we present a simple yet effective clustering scheme with one-pass scan on joint representations to generate large-scale clusters. To mitigate the dependency on external data, a joint training method based on self-supervised learning is introduced. We conduct extensive experiments in both batch and streaming modes. The results show that in the batch mode, TRACER achieves a speedup of at least 2.3× and yields recovery F1-score improvements of 1.7% − 19.6%. In the streaming experimental setup, it achieves 1.1%−27.6% improvement in F1-score, and reduces the average snapshot processing time by up to 84.8%.

Program performance optimization is essential for achieving high execution efficiency, yet it remains a challenging task that requires expertise in both software and hardware. Large Language Models (LLMs), trained on high-quality code from platforms like GitHub and other open-source sources, have shown promise in generating optimized code for simple snippets. However, current LLM-based solutions often fall short when tackling project-level programs due to the complexity of call graphs and the intricate interactions among functions. In this paper, we emulate the process a human expert might follow when optimizing project-level programs and introduce a three-phase framework POLO (PrOject-Level Optimizer) to address this limitation. First, we profile the program to identify performance bottlenecks using an iterative weighting algorithm. Next, we conduct structural analysis by scanning the project and generating a graph that represents the program's structure. Finally, two LLM agents collaborate in iterative cycles to rewrite and optimize the code at these hotspots, gradually improving performance. We conduct experiments on open-source and proprietary projects. The results demonstrate that POLO accurately identifies performance bottlenecks and successfully applies optimizations. Under the O3 compilation flag, the optimized programs achieved speedups ranging from 1.34x to 21.5x.

Out-of-distribution (OOD) node detection in graphs is a critical yet challenging task. Most existing approaches rely heavily on fine-grained labeled data to obtain a pre-trained supervised classifier, inherently assuming the existence of a well-defined pretext classification task. However, when such a task is ill-defined or absent, their applicability becomes severely limited. To overcome this limitation, there is an urgent need to propose a more scalable OOD detection method that is independent of both pretext tasks and label supervision. We harness a new phenomenon called **Feature Resonance**, focusing on the feature space rather than the label space. We observe that, ideally, during the optimization of known ID samples, unknown ID samples undergo more significant representation changes than OOD samples, even when the model is trained to align arbitrary targets. The rationale behind it is that even without gold labels, the local manifold may still exhibit smooth resonance. Based on this, we further develop a novel graph OOD framework, dubbed **R**esonance-based **S**eparation and **L**earning (**RSL**), which comprises two core modules: (i)-a more practical micro-level proxy of feature resonance that measures the movement of feature vectors in one training step. (ii)-integrate with a synthetic OOD node strategy to train an effective OOD classifier. Theoretically, we derive an error bound showing the superior separability of OOD nodes during the resonance period. Extensive experiments on a total of thirteen real-world graph datasets empirically demonstrate that RSL achieves state-of-the-art performance.

Semantic segmentation is crucial in practical applications, especially in autonomous driving. Despite significant advancements in existing semantic segmentation methods, the performance of real-time segmentation approaches remains suboptimal. To address the trade-off between computational efficiency and accuracy in current methods, we propose a novel lightweight real-time semantic segmentation network named MFBPNet. Specifically, this paper introduces three core modules: (1) the Depthwise Separable Convolutional Pyramid Module (DSCPM), which expands the global receptive field and enhances deep feature representation; (2) the Local Attention Refinement Module (LARM), employing channel-wise attention to refine local feature discriminability, particularly for fine-grained objects; and (3) the Boundary Perception Feature Fusion Module (BPFM), which strengthens the feature representation of boundary regions through a multi-level feature fusion mechanism, effectively enhancing the clarity of object boundaries and mitigating boundary blurring issues. Extensive experiments on Cityscapes and CamVid datasets demonstrate that MFBPNet achieves state-of-the-art performance, attaining 75.3% mIoU at 67.3 FPS and 74.3% mIoU at 68.2 FPS, respectively. Compared to existing methods, MFBPNet achieves a superior balance between segmentation accuracy and real-time performance, rendering it highly suitable for autonomous driving systems requiring both real-time processing and high segmentation quality.

Path inference queries over urban-scale camera networks are essential for public safety applications, particularly in emergency scenarios such as suspect pursuit in violent crimes. The objective is to reconstruct the historical movement trajectory of a target object based on a given image query. However, conventional frameworks are often inefficient due to the high computational cost of exhaustive trajectory reconstruction. Moreover, achieving accurate path inference is challenging, as visual matching in real-world environments suffers from inherent uncertainties caused by occlusions, lighting variations, and viewpoint changes. To tackle these challenges, this paper introduces an innovative query-aware path inference framework in large-scale urban videos. The key idea is to eliminate unnecessary trajectory recovery by focusing only on query-relevant data, leveraging spatial-temporal patterns and high-order dependency modeling for accurate and efficient target path inference. We first build a similarity-based index to retrieve candidate vehicle snapshots matching the query, narrowing the search space for subsequent processing. Then we construct a probability motion graph that models the likelihood of transitions between candidate snapshots, effectively incorporating uncertainty and reducing the influence of visual noise. Finally, high-order spatial-temporal dependency constraints are introduced to ensure global consistency and enable robust trajectory extraction. To validate the effectiveness of our approach, we construct four benchmark datasets: two real-world medium-scale datasets collected from deployed urban surveillance systems, and two large-scale synthetic datasets simulating dense urban traffic. Extensive experiments demonstrate that our method significantly outperforms existing baselines in both accuracy and efficiency, offering a promising solution for real-time, large-scale path inference tasks.

The increasing demand for deep neural inference within database environments has driven the emergence of AI?native DBMSs. However, existing solutions either rely on model-centric designs requiring developers to manually select, configure, and maintain models, resulting in high development overhead, or adopt task-centric AutoML approaches with high computational costs and poor DBMS integration. We present MorphingDB, a task-centric AI-native DBMS that automates model storage, selection, and inference within PostgreSQL. To enable flexible, I/O-efficient storage of deep learning models, we first introduce specialized schemas and multi-dimensional tensor data types to support BLOB-based all-in-one and decoupled model storage. Then we design a transfer learning framework for model selection in two phases, which builds a transferability subspace via offline embedding of historical tasks and employs online projection through feature-aware mapping for real-time tasks. To further optimize inference throughput, we propose pre-embedding with vectoring sharing to eliminate redundant computations and DAG-based batch pipelines with cost-aware scheduling to minimize the inference time. Implemented as a PostgreSQL extension with LibTorch, MorphingDB outperforms AI-native DBMSs (EvaDB, Madlib, GaussML) and AutoML platforms (AutoGluon, AutoKeras, AutoSklearn) across nine public datasets, encompassing series, NLP, and image tasks. Our evaluation demonstrates a robust balance among accuracy, resource consumption, and time cost in model selection and significant gains in throughput and resource efficiency.

An effective auto-scaling framework is essential for microservices to ensure performance stability and resource efficiency under dynamic workloads. As revealed by many prior studies, the key to efficient auto-scaling lies in accurately learning performance patterns, i.e., the relationship between performance metrics and workloads in data-driven schemes. However, we notice that there are two significant challenges in characterizing performance patterns for large-scale microservices. Firstly, diverse microservices demonstrate varying sensitivities to heterogeneous machines, causing difficulty in quantifying the performance difference in a fixed manner. Secondly, frequent version upgrades of microservices result in uncertain changes in performance patterns, known as pattern drifts, leading to imprecise resource capacity estimation issues. To address these challenges, we propose Humas, a heterogeneity- and upgrade-aware auto-scaling framework for large-scale microservices. Firstly, Humas quantifies the difference in resource efficiency among heterogeneous machines for various microservices online and normalizes their resources in standard units. Additionally, Humas develops a least-squares density-difference (LSDD) based algorithm to identify pattern drifts caused by upgrades. Lastly, Humas generates capacity adjustment plans for microservices based on the latest performance patterns and predicted workloads. The experiment results conducted on 50 real microservices with over 11,000 containers demonstrate that Humas improves resource efficiency and performance stability by approximately 30.4% and 48.0%, respectively, compared to state-of-the-art approaches.

Multivariate time series forecasting is applied in many domains, such as finance, transportation, and industry. The main challenge of precise forecasting lies in accurately capturing latent dependencies. Recent studies develop various frameworks to reduce computational complexity or to enhance the learning of intricate relationships, while lacking interpretability and generality. In this article, we aim to elucidate the capture of dependencies as the recognition of patterns. We believe that patterns can be formally described from two aspects: the shapes of segments that frequently repeat and the corresponding forms of repetitions. Drawing upon this idea, we design a multivariate time series forecasting model named PRformer , 1 which incorporates a pattern-oriented attention mechanism and a pattern-based projector. The attention mechanism can perceive different forms of repetitions by embedded with various similarity evaluation metrics between segments, and filter out noise from segments to extract potential patterns with a statistical-driven weighting scheme. The pattern-based projector is employed to form the forecasting results by deriving the representative patterns from the set of potential ones. By incorporating explicit definitions of patterns, PRformer is interpretable and general to various time series scenarios. Experimental results on seven datasets demonstrate that PRformer outperforms six state-of-the-art models by about 10.7% in forecasting accuracy.

Data imputation is crucial in the analysis of incomplete time series, such as forecasting and classification, which involves learning dependencies among the observed values to infer missing ones. As there are no ground truths for missing values, the challenge of time series imputation lies in preventing the model from overfitting to spurious correlations. In this article, we believe that ensuring dependency consistency between observed and imputed values in a sequence is paramount for data imputation. Based on this idea, we propose a model called IR 2 -Net , 1 which combines an incomplete representation mechanism (IRM) with an iterative reconstruction framework (IRF) to establish a closed-loop learning-validation imputation paradigm. Firstly, IRM facilitates the representation of dependencies in incomplete sequences while preserving their distributions and semantics, effectively preventing the model from capturing spurious correlations. Secondly, IRF enables the model to reconstruct identical complete sequences separately based on imputed and observed values, ensuring that the dependencies of imputed values remain consistent with those of the observed ones. We conduct experiments on four datasets and compare IR 2 -Net with seven state-of-the-art imputation models. The experiment results show that IR 2 -Net outperforms all the baselines by 4.1%–23.4% in terms of accuracy. Moreover, IRF and IRM are two general modules that can be easily integrated into two existing models, significantly enhancing their performance by 18.3%–42.0%.

Error logs like Java exceptions play a crucial role in diagnosing and resolving errors within the industry. Nonetheless, the extensive logging of Java exceptions may result in exception fatigue in large-scale Java systems at an industrial level, where the frequency of Java exceptions being generated surpasses developers’ ability to manage them effectively. Regrettably, there is a lack of research on the seriousness, prevalence, and solutions to this problem. To close this gap, we first make a comprehensive investigation into the exception fatigue problem within a prominent Internet corporation in China, namely Alibaba, confirming its importance in the industry. Consequently, we introduce a novel solution called ABEL , designed to automatically pinpoint the most relevant exceptions associated with software failures. The key challenge lies in the randomness of exceptions, which prevents existing sequence-based techniques from being effective. To address this challenge, ABEL establishes correlations between Java exceptions and the Key Performance Indicator (KPI) of applications, enabling the identification of exceptions leading to irregularities in KPI. Our evaluation of ABEL across four Java applications and five business KPIs within Alibaba illustrates its capability to pinpoint the primary cause of exception logs with an AC@5 (top-5 accuracy) exceeding 90%, effectively mitigating the exception fatigue problem within Alibaba. Furthermore, it can identify the root-cause exceptions in a real software failure within just 4 minutes, outperforming the manual investigation process by over an hour.

The article focuses on an understudied yet fundamental problem: existing methods typically average the utilization of multiple hardware threads to evaluate the available CPU resources. However, the approach could underestimate the actual usage of the underlying physical core for Simultaneous Multi-Threading (SMT) processors, leading to an overestimation of remaining resources. The overestimation propagates from microarchitecture to operating systems and cloud schedulers, which may misguide scheduling decisions, exacerbate CPU overcommitment, and increase Service Level Agreement (SLA) violations. To address the potential overestimation problem, we propose an SMT-aware and purely data-driven approach namedRemaining CPU(RCPU) that reserves more CPU resources to restrict CPU overcommitment and prevent SLA violations. RCPU requires only a few modifications to the existing cloud infrastructures and can be scaled up to large data centers. Extensive evaluations in the data center proved that RCPU contributes to a reduction of SLA violations by 18% on average for 98% of all latency-sensitive applications. Under a benchmarking experiment, we prove that RCPU increases the accuracy by 69% in terms of Mean Absolute Error (MAE) compared to the state-of-the-art.

Emotion recognition helps teachers to obtain students' emotional states and their learning progress in their study. Many deep learning-based technologies, such as convolutional neural networks (CNN) and large language models (LLM) models are used for emotion recognition and prediction with learning data of students. An emotion recognition and prediction for online learning students using deep learning approaches is proposed, namely EPLLM. The method transforming the students' data, such as forum texts, questions, and answers, to a sequential form and extracts feature information from students' data using deep learning models with their behavioral changes in online learning. The student emotions are recognized and predicted based online learning data with combination of the deep learning models. To verify the performances of the model, many experiments are conducted using the public dataset. The results verify that, the model achieved better effectiveness in emotion prediction, compared with existing models. The values of F1 score of the proposed model is improved 0.051 compared that of the exist SGNN-LLM model.

with the rapid development of artificial intelligence (AI) and Large Language Models (LLM) technologies, it offers innovative approaches to model and analyze to predict student performance with educational behavior and learning data. But the challenges of data diversity, technical complex, and lack of semantic comprehension ability that limited the use of AI-based tools for learning performance prediction. In the paper, student emotions recognition based online learning data especially forum texts using LLMs is proposed, and an improved online learning performance prediction with online learning data, including student emotions using Signed Graph Neural Networks (SGNN) and LLMs, namely ER-SGNN-LLM, is constructed. In the model, the keywords are extracted from both forum texts and answers generated by students using LLM, and the keywords extracted from student’s forum texts are used for student emotions recognition, the keywords extracted from student’s answers, as well as the student emotions are used for student learning prediction. The relationships between each keyword extracted from texts and knowledge points of the course are encoded with SGNN. A graphic contrastive learning model is used to handle the noise in the dataset caused by students' subjective reasons. The combination of GNN and LLM is used to student emotions recognition and learning prediction. To verify the performances of the model, many experiments are conducted using the public dataset. The results demonstrate that, the model achieved better effectiveness in learning prediction, compared with other models. The values of F1 score of the proposed model is improved 0.032 compared that of the exist SGNN-LLM model.

Object Goal Navigation is a task that seeks to allow intelligent agents to locate and navigate to a particular object goal in an unfamiliar environment. However, the current goal-oriented semantic policy, which is based on deep reinforcement learning (DRL), has difficulty in retaining long-term object semantic information and lacks adequate goal-oriented ability. This leads to intelligent agents having to extensively explore their environment in order to locate a goal, resulting in inefficient navigation. To address these challenges, this paper proposes a goal-oriented semantic policy based on multi-headed self-attention (MHSA) to improve the efficiency of object navigation. By using the self-attention mechanism, the policy can automatically learn and extract features relevant to goal navigation without the need for manual feature extractor design. Multiple attention heads can simultaneously focus on various semantic features to extract vital information about the objective goal. We propose a novel object-goal navigation model called SemGO based on this policy. The SemGO model is proficient at managing environments with intricate semantic structures. It can detect the correlation between global and local information, which improves navigation accuracy significantly. Additionally, it has superior generalization capabilities, making it adaptable to changes in different object goals and environments. The experimental results show that the SemGO model achieves a SPL of 0.324, a success rate of 0.635, and a reduction of DTS to 1.601m in the Gibson dataset for object-goal navigation.

Co-locating online latency-critical (LC) services with best-effort (BE) batch jobs in the same server has been widely adopted by modern data centers to improve resource utilization. Various approaches have been proposed to maximize the resources allocated to the BE jobs without SLO (service level objective) violation. However, when facing bursty workloads, existing solutions suffer from poor performance because they cannot react promptly to the sudden and sharp increase of LC service requests. Consequently, these methods result in either a high violation rate of the SLO constraint or low resource utilization caused by conservative allocation strategies.

Software deployment misconfiguration often happens and has been one of the major causes of deployment failures that give rise to service interruptions. However, there is currently no existing approach to automatically repairing deployment failures. We propose DeployFix, which automatically repairs software deployment failures via constraint solving in the dynamic-changing deployment environments. DeployFix first defines DeployIR as a unified intermediate representation to achieve the translation of heterogeneous specifications from different schedulers with different syntaxes. By reducing the root-cause analysis of deployment failures to the conflict resolution in propositional logic, DeployFix uses off-the-shelf constraint solvers to achieve automatic localization and diagnosis of conflicting constraints, which are the root causes of deployment failures. DeployFix finally resolves the conflicting constraints and generates repaired deployment configurations in terms of practical requirements. We evaluate DeployFix in both simulation and production environments with tens of thousands of nodes at Alibaba, on which tens of thousands of applications are running guided by hundreds of thousands of deployment constraints. Experimental results demonstrate that DeployFix outperforms the state of the art and it correctly repairs the deployment failures in minutes, even in a large production data center.

Abstract Navigation in unknown 3D environments aims to progressively find an efficient path to a given target goal in unseen scenarios. A challenge is how to explore the navigation quickly and effectively. An end-to-end learning approach has been proposed to extract geometric shapes from RGB images, but it is not suitable for large environments due to its exhaustive exploration with exponential search space. Active Neural SLAM (ANS) presents a Neural SLAM module to maximize the exploration coverage to tackle the active SLAM task. However, ANS still frequently visits the explored areas due to the inappropriate local target selection. In this paper, we propose a Neural Attention-based Visual SLAM (NAVS) model to explore unknown 3D environments. Spatial attention is provided to quickly identify obstacles (such as similarly colored tea table or floor). We also leverage the priority of unknown regions in the short-term goal decision to avoid frequent exploration with a channel attention. The experimental results show that our model can build a more accurate map than ANS and other baseline methods with less running time. In terms of relative coverage, NAVS achieves a 0.5 $$\%$$ % improvement over ANS in overall and a 1.1 $$\%$$ % improvement over ANS in large environments.

Aiming at the problems of difficulty in extracting key features and low prediction accuracy of traditional convolutional neural networks in Chinese speech recognition, we analyze the impacts of information leakage and unstandardized phoneme features on its performance, based on the deep convolutional neural network (DCNN)-connectionist temporal classification (CTC) model. In addition, a multi-core two dimensional causal convolution fusion network layer structure of SKNet is constructed, and we propose a DCNN-CTC model for fusion of attention mechanism and SKNet multi-core 2D causal convolution network (ASKCC-DCNN-CTC), which effectively improves the accuracy and training speed of Chinese speech recognition. The simulation results show that the error rate of our model on the ST-CMDS dataset is 12.201% lower than that of the DCNN-CTC model, the performance on the THCHS30 dataset is also improved, which reveals a good generalization ability.

Efficient localization plays a significant role in mobile autonomous robots’ navigation systems. Traditional visual simultaneous localization systems based on point feature matching suffer from two shortcomings. First one is that the method of tracking features is not robust for the environments with frequent changes in brightness. Another one is the large of consecutive visual keyframes consume expensive computation and storage resources in complex environments. To solve these problems, we propose an end-to-end visual localization algorithm to solve the robust and efficiency challenges via a deep learning mode. Firstly, we perform preprocessing operations such as cropping, averaging, and timestamp alignment on datasets to reduce computational cost and time. Secondly, we use CNN networks to autonomously learn the correct features for localization, which is robust to illumination changes. Finally, we utilize LSTM networks to memorize global trajectories to improve the localization precision. We performed a broad range of experiments on both indoor and outdoor datasets. The experimental results demonstrate that the translation and orientation accuracy in outdoor scenes improved by 32.9% and 31.4%, respectively. The average improvement of translation positioning accuracy in indoor scenes is 38.4%, and the orientation improvement is 13.1%. Moreover, the effectiveness of predicting the global motion trajectories of sequential images algorithm has been verified and is superior to other CNN methods.

A fault in large online service systems often triggers numerous alerts due to the complex business and component dependencies among services, which is known as “alert storm”. In a short time, an online service system may generate a huge amount of alert data. This poses a challenge for on-call engineers to identify alerts that are associated with a system failure for root cause analysis. In this paper, we propose DyAlert, a dynamic graph neural networks-based approach for linking alerts that might be triggered by a same fault to reduce the burden of on-call engineers in the fault analysis. Our insight is that alerts are often triggered by alert propagation when a system failure occurs, e.g., alert$a$would lead to the occurrence of alert$b$. Whether two alerts should be linked depends on if one alert is triggered by the propagation of the other. Leveraging this insight, we design a dynamic graph (namely Alert-Metric Dynamic Graph) that describes the propagation process of alerts. Based on the dynamic graph, we train a neural networks-based model to predict alert links. We evaluate DyAlert with real-world data collected from an online service system running 85 business units and about 30,000 different services in a large enterprise. The results show that DyAlert is effective in predicting alert links and it outperforms the state-of-the-art approaches with an average increase of 0.259 in F1-score.

Accurately forecasting workloads in terms of throughput that is quantified as queries per second (QPS) is essential for microservices to elastically adjust their resource allocations. However, long-term QPS prediction is challenging in two aspects: 1) generality across various services with different temporal patterns, 2) characterization of intricate QPS sequences which are entangled by multiple components. In this paper, we propose a knowledge auto-embedding Informer network (KAE-Informer) for forecasting the long-term QPS sequences of microservices. By analyzing a large number of microservice traces, we discover that there are two main decomposable and predictable components in QPS sequences, namely global trend & dominant periodicity (TP) and low-frequency residual patterns with long-range dependencies. These two components are important for accurately forecasting long-term QPS. First, KAE-Informer embeds the knowledge of TP components through mathematical modeling. Second, KAE-Informer designs a convolution ProbSparse self-attention mechanism and a multi-layer event discrimination scheme to extract and embed the knowledge of local context awareness and event regression effect implied in residual components, respectively. We conduct experiments based on three real datasets including a QPS dataset collected from 40 microservices. The experiment results show that KAE-Informer achieves a reduction of MAPE, MAE and RMSE by about 16.6%, 17.6% and 23.1% respectively, compared to the state-of-the-art models.

Real-time traffic estimation focuses on predicting the travel time of one travel path, which is capable of helping drivers selecting an appropriate or favor path. Statistical analysis or neural network approaches have been explored to predict the travel time on a massive volume of traffic data. These methods need to be updated when the traffic varies frequently, which incurs tremendous overhead. We build a system RealTER⁢e⁢a⁢l⁢T⁢E, implemented on a popular and open source streaming system StormS⁢t⁢o⁢r⁢m to quickly deal with high speed trajectory data. In RealTER⁢e⁢a⁢l⁢T⁢E, we propose a locality-sensitive partition and deployment algorithm for a large road network. A histogram estimation approach is adopted to predict the traffic. This approach is general and able to be incremental updated in parallel. Extensive experiments are conducted on six real road networks and the results illustrate RealTE achieves higher throughput and lower prediction error than existing methods. The runtime of a traffic estimation is less than 11 seconds over a large road network and it takes only 619619 microseconds for model updates.

The problem of identifying the k -shortest paths (KSPs for short) in a dynamic road network is essential to many location-based services. Road networks are dynamic in the sense that the weights of the edges in the corresponding graph constantly change over time, representing evolving traffic conditions. Very often such services have to process numerous KSP queries over large road networks at the same time, thus there is a pressing need to identify distributed solutions for this problem. However, most existing approaches are designed to identify KSPs on a static graph in a sequential manner (i.e., the (i+1)-th shortest path is generated based on the i-th shortest path), restricting their scalability and applicability in a distributed setting. We therefore propose KSP-DG, a distributed algorithm for identifying k-shortest paths in a dynamic graph. It is based on partitioning the entire graph into smaller subgraphs, and reduces the problem of determining KSPs into the computation of partial KSPs in relevant subgraphs, which can execute in parallel on a cluster of servers. A distributed two-level index called DTLP is developed to facilitate the efficient identification of relevant subgraphs. A salient feature of DTLP is that it indexes a set of virtual paths that are insensitive to varying traffic conditions, leading to very low maintenance cost in dynamic road networks. This is the first treatment of the problem of processing KSP queries over dynamic road networks. Extensive experiments conducted on real road networks confirm the superiority of our proposal over baseline methods.

The ubiquitousness of GPS sensors in smart-phones, vehicles and wearable devices has enabled the collection of massive volumes of trajectory data from tracing moving objects. Consequently, an unprecedented scale of timestamped GPS data has been generated and posed an urgent demand for an effective storage mechanism for trajectory databases. The mainstream compression technique is called trajectory simplification, that finds a subsequence to approximate the original trajectory and attempts to minimize the information loss under a distance measure. Even though various simplification algorithms have been proposed in the past decades, there still lacks a thorough comparison to cover all the state-of-the-art algorithms and evaluate their quality using datasets in diversified motion patterns. Hence, it still remains a challenge for GPS data collectors to determine a proper algorithm in a concrete application. In addition, almost the entire line of previous methods uses error-based metrics to evaluate the compression quality, while ignoring their usability in supporting spatio-temporal queries on top of the reduced database. To bridge these gaps, we conduct so far the most comprehensive evaluation on trajectory simplification techniques. We compare the performance of 25 algorithms in total using five real datasets in different motion patterns. According to the experimental findings, we present useful guidance for the selection or development of effective trajectory simplification algorithms.

In the real-world environment, users have sufficient experience in their focused domains but lack experience in other domains. Recommender systems are very helpful for recommending potentially desirable items to users in unfamiliar domains, and cross-domain collaborative filtering is therefore an important emerging research topic. However, it is inevitable that the cold-start issue will be encountered in unfamiliar domains due to the lack of feedback data. The Bayesian approach shows that priors play an important role when there are insufficient data, which implies that recommendation performance can be significantly improved in cold-start domains if informative priors can be provided. Based on this idea, we propose a Weighted Irregular Tensor Factorization (WITF) model to leverage multi-domain feedback data across all users to learn the cross-domain priors w.r.t. both users and items. The features learned from WITF serve as the informative priors on the latent factors of users and items in terms of weighted matrix factorization models. Moreover, WITF is a unified framework for dealing with both explicit feedback and implicit feedback. To prove the effectiveness of our approach, we studied three typical real-world cases in which a collection of empirical evaluations were conducted on real-world datasets to compare the performance of our model and other state-of-the-art approaches. The results show the superiority of our model over comparison models.

Shortest path query over a dynamic road network is a prominent problem for the optimization of real-time traffic systems. Existing solutions rely either on a centralized index system with tremendous pre-computation overhead, or on a distributed graph processing system such as Pregel that requires much synchronization effort. However, the performance of these systems degenerates with frequent route path updates caused by continuous traffic condition change. In this paper, we build CANDS, a distributed stream processing platform for continuous optimal shortest path queries. It provides an asynchronous solution to answering a large quantity of shortest path queries. It is able to efficiently detect affected paths and adjust their paths in the face of traffic updates. Moreover, the affected paths can be quickly updated to the optimal solutions throughout the whole navigation process. Experimental results demonstrate that the performance for answering shortest path queries by CANDS is two orders of magnitude better than that of GPS, an open-source implementation of Pregel. In addition, CANDS provides fast response to traffic updates to guarantee the optimality of answering shortest path queries.