Can SSDs help reduce random I/Os in Hash Joins?

A hybrid drive combines the features of SSDs and HDDs in the same unit by using SSD as the intermediate cache. In light of its promising features, we propose a new algorithm called CGHJ(Cached Grace Hash Join) for hybrid drives, which reduces hard disk random I/Os that occur in the partitioning phase of traditional Grace hash joins by caching the segments of buckets in the SSD and migrating these segments of each partition contiguously to the HDD. Experiment results show that CGHJ can greatly reduce random disk I/Os in the case of small joining working spaces or larger relations and improve hash join performance.