Description

TID hash joins are a simple and memory-efficient method for processing large join queries. They are based on standard hash join algorithms but only store TID/key pairs in the hash table instead of entire tuples. This typically reduces memory requirements by more than an order of magnitude bringing substantial benefits. In particular, performance for joins on Giga-Byte relations can substantially be improved by reducing the amount of disk I/O to a large extent. Furthermore, efficient processing of mixed multi-user workloads consisting of both join queries and OLTP transactions is supported. We present a detailed simulation study to analyze the performance of TID hash joins. In particular, we identify the conditions under which TID hash joins are most beneficial. Furthermore, we compare TID hash join with adaptive hash join algorithms that have been proposed to deal with mixed workloads.