Efficient query evaluation on distributed graphs with Hadoop environment

Graph has emerged as a powerful data structure to describe various data. Query evaluation on distributed graphs takes much cost due to the complexity of links among sites. Dan Suciu has proposed algorithms for query evaluation on semistructured data that is a rooted, edge-labeled graph, and algorithms are proved to be efficient in terms of communication steps and data transferring during the evaluation. However, one disadvantage is that communication data are collected to one single site, which leads to a bottleneck in the evaluation for real-life data. In this paper, we propose two algorithms to improve Dan Suciu's algorithms: one-pass algorithm is to significantly reduce a large amount of redundant data in the evaluation, and iterₐcc algorithm is to resolve the bottleneck. Then, we design an efficient implementation with only one MapReduce job for our algorithms in Hadoop environment by utilizing features of Hadoop file system. Experiments on cloud system show that one-pass algorithm can detect and remove 50% of data being redundant in the evaluation process on YouTube and DBLP datasets, and iterₐcc algorithm is running without the bottleneck even when we double the size of input data.