A data-parallel framework is very attractive for large-scale data processing since it enables such an application to easily process a huge amount of data on commodity machines. MapReduce, a popular data-parallel framework, is used in various fields such as web search, data mining and data warehouses; it is proven to be very practical for such a data-parallel application. A star-join query is a popular query in data warehouses that are a current target domain of data-parallel frameworks. This article proposes a new algorithm that efficiently processes star-join queries in data-parallel frameworks such as MapReduce and Dryad. Our star-join algorithm for general data-parallel frameworks is called Scatter-Gather-Merge, and it processes star-join queries in a constant number of computation steps, although the number of participating dimension tables increases. By adopting bloom filters, Scatter-Gather-Merge reduces a non-trivial amount of IO. We also show that Scatter-Gather-Merge can be easily applied to MapReduce. Our experimental results in both cluster and cloud environments show that Scatter-Gather-Merge outperforms existing approaches.
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