Abstract
Building cloud data-intensive applications often requires usingmultiple data stores (NoSQL, HDFS, RDBMS, etc.), each optimised forone kind of data and tasks. However, the wide diversification of data storeinterfaces makes it difficult to access and integrate data from multiple datastores. This important problem has motivated the design of a new generation ofsystems, called multistore systems, which provide integrated or transparentaccess to a number of cloud data stores through one or more query languages.In this paper, we give an overview of query processing in multistore systems.We start by introducing the recent cloud data management solutions andquery processing in multidatabase systems. Then, we describe and analysesome representative multistore systems, based on their architecture, data model,query languages and query processing techniques. To ease comparison, wedivide multistore systems based on the level of coupling with the underlyingdata stores, i.e., loosely-coupled, tightly-coupled and hybrid. Our analysisreveals some important trends, which we discuss. We also identify some majorresearch issues.