Query optimization on hybrid storage

Thanks to the rapid growth of memory capacity, it is now feasible to perform query processing completely in memory. Nevertheless, as main memory is substantially more expensive than most secondary storage equipments, including HDD and SSD, it is not suitable for storing cold data. Therefore, a hybrid data storage composed of both memory and secondary storage is expected to stay popular in the foreseeable future. In this paper, we introduce a query optimization model for hybrid data storage. Different from traditional query processors, which treat either main memory as a cache or secondary storage as an anti-cache, our model performs semantic data partitioning between memory and secondary storage. Query optimization can thus take the partitioning of data into account, to achieve enhanced performance. We conducted experimental evaluation on a columnar query engine to demonstrate the advantage of the proposed approach.