With the rapid growth of graphs in different applications, it is inevitable to leverage existing distributed data processing frameworks in managing large graphs. Although these frameworks ease the developing cost, it is still cumbersome and error-prone for developers to implement complex graph analysis tasks in distributed environments. Additionally, developers have to learn the details of these frameworks quite well, which is a key to improve the performance of distributed jobs. This paper introduces a high level query language called GLog and proposes its evaluation method to overcome these limitations. Specifically, we first design a RG (Relational-Graph) data model to mix relational data and graph data, and extend Datalog to GLog on RG tables to support various graph analysis tasks. Second, we define operations on RG tables, and show translation templates to convert a GLog query into a sequence of MapReduce jobs. Third, we propose two strategies, namely rule merging and iteration rewriting, to optimize the translated jobs. The final experiments show that GLog can not only express various graph analysis tasks in a more succinct way, but also achieve a better performance for most of the graph analysis tasks than Pig, another high level dataflow system.

Continuous pattern detection plays an important role in monitoring-related applications. The large size and dynamic update of graphs, along with the massive search space, pose huge challenges in developing an efficient continuous pattern detection system. In this paper, we leverage a distributed graph processing framework to approximately detect a given pattern over a large dynamic graph. We aim to improve the scalability and precision, and reduce the response time and message cost in the detection. We convert a given query pattern into a Single-Sink DAG (Directed Acyclic Graph), and propose an evaluation plan with message transitions on the DAG, which is shorten by SSD plan, to detect the pattern in a large dynamic graph. SSD plan can guide the data graph exploration via messages, and the messages will converge at data sink vertices, which then detect existences of the query pattern. We also conduct join operations over partial vertices during the graph exploration to improve the precision of pattern detection. In addition, we show that SSD plan can support the continuous query over dynamic graphs with slight extensions. We further design various sink vertex selection strategies and neighborhood based transition rule attachment to lower the evaluation cost. The experiments on billion-edge real-life graphs using Giraph, an open source implementation of Pregel, illustrate the efficiency and effectiveness of our method.

This paper takes the shortest path discovery to study efficient relational approaches to graph search queries. We first abstract three enhanced relational operators, based on which we introduce an FEM framework to bridge the gap between relational operations and graph operations. We show new features introduced by recent SQL standards, such as window function and merge statement, can improve the performance of the FEM framework. Second, we propose an edge weight aware graph partitioning schema and design a bi-directional restrictive BFS (breadth-first-search)over partitioned tables, which improves the scalability and performance without extra indexing overheads. The final extensive experimental results illustrate our relational approach with optimization strategies can achieve high scalability and performance.

With the advent of cloud computing, it becomes desirable to utilize cloud computing to efficiently process complex operations on large graphs without compromising their sensitive information. This paper studies shortest distance computing in the cloud, which aims at the following goals: i) preventing outsourced graphs from neighborhood attack, ii) preserving shortest distances in outsourced graphs, iii) minimizing overhead on the client side. The basic idea of this paper is to transform an original graph G into a link graph Gl kept locally and a set of outsourced graphs Go. Each outsourced graph should meet the requirement of a new security model called 1-neighborhood-d-radius. In addition, the shortest distance query can be answered using Gl and Go. Our objective is to minimize the space cost on the client side when both security and utility requirements are satisfied. We devise a greedy method to produce Gl and Go, which can exactly answer the shortest distance queries. We also develop an efficient transformation method to support approximate shortest distance answering under a given additive error bound. The final experimental results illustrate the effectiveness and efficiency of our method.

With the rapid growth of large graphs, we cannot assume that graphs can still be fully loaded into memory, thus the disk-based graph operation is inevitable. In this paper, we take the shortest path discovery as an example to investigate the technique issues when leveraging existing infrastructure of relational database (RDB) in the graph data management. Based on the observation that a variety of graph search queries can be implemented by iterative operations including selecting frontier nodes from visited nodes, making expansion from the selected frontier nodes, and merging the expanded nodes into the visited ones, we introduce a relational FEM framework with three corresponding operators to implement graph search tasks in the RDB context. We show new features such as window function and merge statement introduced by recent SQL standards can not only simplify the expression but also improve the performance of the FEM framework. In addition, we propose two optimization strategies specific to shortest path discovery inside the FEM framework. First, we take a bi-directional set Dijkstra's algorithm in the path finding. The bi-directional strategy can reduce the search space, and set Dijkstra's algorithm finds the shortest path in a set-at-a-time fashion. Second, we introduce an index named SegTable to preserve the local shortest segments, and exploit SegTable to further improve the performance. The final extensive experimental results illustrate our relational approach with the optimization strategies achieves high scalability and performance.