⬢ Graph Processing & Analytics

Shuangyan Yang, Minjia Zhang, Wenqian Dong and 1 other

The Graph Neural Network (GNN) is showing outstanding results in improving the performance of graph-based applications. Recent studies demonstrate that GNN performance can be boosted via using more advanced aggregators, deeper aggregation depth, larger sampling rate, etc. While leading to promising results, the improvements come at a cost of significantly increased memory footprint, easily exceeding GPU memory capacity. In this paper, we introduce a method, Betty, to make GNN training more scalable and accessible via batch-level partitioning. Different from DNN training, a mini-batch in GNN has complex dependencies between input features and output labels, making batch-level partitioning difficult. Betty introduces two noveltechniques, redundancy-embedded graph (REG) partitioning and memory-aware partitioning, to effectively mitigate the redundancy and load imbalances issues across the partitions. Our evaluation of large-scale real-world datasets shows that Betty can significantly mitigate the memory bottleneck, enabling scalable GNN training with much deeper aggregation depths, larger sampling rate, larger training batch sizes, together with more advanced aggregators, with a few as a single GPU.

Mahbod Afarin, Chao Gao, Shafiur Rahman and 2 others

We consider the problem of graph analytics on evolving graphs (i.e., graphs that change over time). In this scenario, a query typically needs to be applied to different snapshots of the graph over an extended time window, for example to track the evolution of a property over time. Solving a query independently on multiple snapshots is inefficient due to repeated execution of subcomputation common to multiple snapshots. At the same time, we show that using streaming, where we start from the earliest snapshot and stream the changes to the graph incrementally updating the query results one snapshot at a time is also inefficient. We propose CommonGraph, an approach for efficient processing of queries on evolving graphs. We first observe that deletion operations are significantly more expensive than addition operations for many graph queries (those that are monotonic). CommonGraph converts all deletions to additions by finding a common graph that exists across all snapshots. After computing the query on this graph, to reach any snapshot, we simply need to add the missing edges and incrementally update the query results. CommonGraph also allows sharing of common additions among snapshots that require them, and breaks the sequential dependency inherent in the traditional streaming approach where snapshots are processed in sequence, enabling additional opportunities for parallelism. We incorporate the CommonGraph approach by extending the KickStarter streaming framework. We implement optimizations that enable efficient handling of edge additions without resorting to expensive in place graph mutations, significantly reducing the streaming overhead, and enabling direct reuse of shared edges among different snapshots. CommonGraph achieves 1.38x-8.17x improvement in performance over Kickstarter across multiple benchmarks.

Yangjie Zhou, Jingwen Leng, Yaoxu Song and 9 others

As graph neural networks (GNNs) have achieved great success in many graph learning problems, it is of paramount importance to support their efficient execution. Different graphs and different operators present different patterns during execution. However, there is still a gap in the existing GNN acceleration research to explore adaptive parallelism. We show that existing GNN frameworks rely on handwritten static kernels, which fail to achieve the best performance across different graph operators and input graph structures. In this work, we propose uGrapher, a unified interface that achieves general high performance for different graph operators and datasets. The existing GNN frameworks can easily integrate our design for its simple and unified API. We take a principled approach that decouples a graph operator’s computation and schedule to achieve that. We first build a GNN-specific operator abstraction that incorporates the semantics of graph tensors and graph loops. We explore various schedule strategies based on the abstraction that can balance the well-established trade-off relationship between parallelism, locality, and efficiency. Our evaluation shows that uGrapher can bring up to 29.1× (3.5× on average) performance improvement over the state-of-the-art baselines on two studied NVIDIA GPUs.

Xizhe Yin, Zhijia Zhao and Rajiv Gupta

In concurrent graph processing, different queries are evaluated on the same graph simultaneously, sharing the graph accesses via the memory hierarchy. However, different queries may traverse the graph differently, especially for those starting from different source vertices. When these graph traversals are ”misaligned”, the benefits of graph access sharing can be seriously compromised. As more concurrent queries are added to the evaluation batch, the issue tends to become even worse.

Jingji Chen and Xuehai Qian

This paper proposes Khuzdul, a distributed execution engine with a well-defined abstraction that can be integrated with existing single-machine graph pattern mining (GPM) systems to provide efficiency and scalability at the same time. The key novelty is the extendable embedding abstraction which can express pattern enumeration algorithms, allow fine-grained task scheduling, and enable low-cost GPM-specific data reuse to reduce communication cost. The effective BFS-DFS hybrid exploration generates sufficient concurrent tasks for communication-computation overlapping with bounded memory consumption. Two scalable distributed GPM systems are implemented by porting Automine and GraphPi on Khuzdul. Our evaluation shows that Khuzdul based systems significantly outperform state-of-the-art distributed GPM systems with partitioned graphs by up to 75.5× (on average 19.0×), achieve similar or even better performance compared with the fastest distributed GPM systems with replicated graph, and scale to massive graphs with more than one hundred billion edges with a commodity cluster.

Jingji Chen and Xuehai Qian

Graph pattern mining (GPM) is an important application that identifies structures from graphs. Despite the recent progress, the performance gap between the state-of-the-art GPM systems and an efficient algorithm—pattern decomposition—is still at least an order of magnitude. This paper clears the fundamental obstacles of adopting pattern decomposition to a GPM system.

Jackson Melchert, Kathleen Feng, Caleb Donovick and 6 others

The architecture of a coarse-grained reconfigurable array (CGRA) processing element (PE) has a significant effect on the performance and energy-efficiency of an application running on the CGRA. This paper presents APEX, an automated approach for generating specialized PE architectures for an application or an application domain. APEX first analyzes application domain benchmarks using frequent subgraph mining to extract commonly occurring computational subgraphs. APEX then generates specialized PEs by merging subgraphs using a datapath graph merging algorithm. The merged datapath graphs are translated into a PE specification from which we automatically generate the PE hardware description in Verilog along with a compiler that maps applications to the PE. The PE hardware and compiler are inserted into a flexible CGRA generation and compilation toolchain that allows for agile evaluation of CGRAs. We evaluate APEX for two domains, machine learning and image processing. For image processing applications, our automatically generated CGRAs with specialized PEs achieve from 5% to 30% less area and from 22% to 46% less energy compared to a general-purpose CGRA. For machine learning applications, our automatically generated CGRAs consume 16% to 59% less energy and 22% to 39% less area than a general-purpose CGRA. This work paves the way for creation of application domain-driven design-space exploration frameworks that automatically generate efficient programmable accelerators, with a much lower design effort for both hardware and compiler generation.

Yufeng Wang and Charith Mendis

In recent years, Temporal Graph Neural Networks (TGNNs) have achieved great success in learning tasks for graphs that change over time. These dynamic/temporal graphs represent topology changes as either discrete static graph snapshots (called DTDGs), or a continuous stream of timestamped edges (called CTDGs). Because continuous-time graphs have richer time information, it will be crucial to have abstractions for programming CTDG-based models so that practitioners can easily explore new designs and optimizations in this space. A few recent frameworks have been proposed for programming and accelerating TGNN models, but these either do not support continuous-time graphs, lack easy composability, and/or do not facilitate CTDG-specific optimizations.

Tsun-Yu Yang, Cale England, Yi Li and 2 others

As graphs exponentially grow recently, out-of-core graph systems have been invented to process large-scale graphs by keeping massive data in storage. Among them, many systems process the graphs iteration-by-iteration and provide synchronous semantics that allows easy programmability by forcing the computation dependency of vertex values between iterations. On the other hand, although future value computation is an effective IO optimization for out-of-core graph systems by computing vertex values of future iterations in advance, it is challenging to take full advantage of future value computation while guaranteeing iteration-based dependency. In fact, based on our investigation, even state-of-the-art work along this direction has a wide gap from optimality in IO reduction and further requires substantial overhead in computation as well as extra memory consumption.

Hongtao Chen, Mingxing Zhang, Ke Yang and 4 others

Many real-time OLAP systems have been proposed to query evolving data with sub-second latency. Although this feature is highly attractive, it is very hard to be achieved on analytic graph queries that can only be answered after accessing every connected vertex. Fortunately, researchers recently observed that answering pairwise queries is enough for many real-world scenarios. These pairwise queries avoid the exhaustive nature and hence may only need to access a small portion of the graph. Obviously, the crux of achieving low latency is to what extent the system can eliminate unnecessary computations. This pruning process, according to our investigation, is usually achieved by estimating certain upper bounds of the query result in existing systems.

Shuke Wang, Mingxing Zhang, Ke Yang and 4 others

Out-of-core random walk system has recently attracted a lot of attention as an economical way to run billions of walkers over large graphs. However, existing out-of-core random walk systems are all built upon general out-of-core graph processing frameworks, and hence do not take advantage of the unique properties of random walk applications. Different from traditional graph analysis algorithms, the sampling process of random walk can be decoupled from the processing of the walkers. It enables the system to reserve only pre-sample results in memory, which are typically much smaller than the entire edge set. Moreover, in random walk, it is not the number of walkers but the number of steps moved per second that dominates the overall performance. Thus, with independent walkers, there is no need to process all the walkers simultaneously.

Zeyu Zhu, Peisong Wang, Qinghao Hu and 3 others

Graph Neural Networks (GNNs) have shown great superiority on non-Euclidean graph data, achieving ground-breaking performance on various graph-related tasks. As a practical solution to train GNN on large graphs with billions of nodes and edges, the sampling-based training is widely adopted by existing training frameworks. However, through an in-depth analysis, we observe that the efficiency of existing sampling-based training frameworks is still limited due to the key bottlenecks lying in all three phases of sampling-based training, i.e., subgraph sample, memory IO, and computation. To this end, we propose FastGL, a GPU-efficient Framework for accelerating sampling-based training of GNN at Large scale by simultaneously optimizing all above three phases, taking into account both GPU characteristics and graph structure. Specifically, by exploiting the inherent overlap within graph structures, FastGL develops the Match-Reorder strategy to reduce the data traffic, which accelerates the memory IO without incurring any GPU memory overhead. Additionally, FastGL leverages a Memory-Aware computation method, harnessing the GPU memory's hierarchical nature to mitigate irregular data access during computation. FastGL further incorporates the Fused-Map approach aimed at diminishing the synchronization overhead during sampling. Extensive experiments demonstrate that FastGL can achieve an average speedup of 11.8×, 2.2× and 1.5× over the state-of-the-art frameworks PyG, DGL, and GNNLab, respectively. Our code is available at https://github.com/a1bc2def6g/fastgl-ae.

Hochan Lee, Roshan Dathathri and Keshav Pingali

Most distributed graph analytics systems such as Gemini, Gluon, and SympleGraph support a computational model in which node properties are updated iteratively using properties of adjacent neighbors of those nodes. However, there are many algorithms that cannot be expressed in this model, such as the Louvain algorithm for community detection and the Shiloach-Vishkin algorithm for connected components. These algorithms may be more efficient or may produce better quality output than simpler algorithms that can be expressed using updates only from adjacent vertices.

Yuyu Chen and Zhongxing Yu

Recent years have witnessed an ever-growing usage of graph database management systems (GDBMSs) in various data-driven applications. Query optimization aims to improve the performance of database queries by identifying the most efficient way to execute them, and is an important stage of GDBMS workflow. Like other sophisticated systems, such as compilers, the query optimization process is complex and its implementation is prone to bugs. This paper conducts the first characteristic study of query optimization bugs in GDBMSs, including the root causes, manifestation methods, and fix strategies, and delivers 10 novel and important findings about them. Based on the characteristic study, we also developed a testing tool tailored to uncover GDBMS query optimization bugs, and the tool found 20 unique GDBMS bugs, 10 of which are query optimization bugs.

Weiyu Xie, Mingxing Zhang, Xia Liao and 3 others

Variable-Length Graph Pattern Matching (VLGPM) is a critical functionality in graph databases, pivotal for identifying patterns where the number of connecting edges between two matched vertices is variable. This function plays a vital role in analyzing complex and dynamic networks such as social networks or bank transfers networks, where relationships can vary extensively in both length and structure. However, despite its importance, current graph databases, optimized primarily for single-hop subgraph matching, struggle with VLGPM over large graphs.

Yiqing Wang, Hailong Yang, Kejie Ma and 8 others

Temporal Graph Network (TGN) is increasingly adopted to model evolving relationships in dynamic graphs. However, the training pipeline is plagued by pervasive redundancy in computation, storage, and data loading. These redundancies harm computational efficiency, exacerbate memory pressure, and induce excessive CPU-GPU data transfers. We present PULSE, an end-to-end TGN training framework that systematically eliminates redundancies guided by a unified minimal-unit principle. To realize such principle, PULSE defines three synergetic units: 1) the Minimal Input Unit (MIU) for component-wise deduplication and operator-level reconstruction of redundant computations, 2) the Minimal Storage Unit (MSU) for dependency-guided message reconstruction, only preserving irreproducible entries while enabling on-demand recovery of others, and 3) the Minimal Reuse Unit (MRU) for GPU memory management, combining a BlockPool-based buffer allocator with a bipartite temporal reuse strategy to mitigate fragmentation and exploit inter-batch locality. Experimental results on representative benchmarks demonstrate that PULSE improves training throughput by up to 6.67× over the state-of-the-art baselines.