Efficient Join Synopsis Maintenance for Data Warehouse

Various sources such as daily business operations and sensors from different IoT applications constantly generate a lot of data. They are often loaded into a data warehouse system to perform complex analysis over. It, however, can be extremely costly if the query involves joins, especially many-to-many joins over multiple large tables. A join synopsis, i.e., a small uniform random sample over the join result, often suffices as a representative alternative to the full join result for many applications such as histogram construction, model training and etc. Towards that end, we propose a novel algorithm SJoin that can maintain a join synopsis over a pre-specified general θ-join query in a dynamic database with continuous inflows of updates. Central to SJoin is maintaining a weighted join graph index, which assists to efficiently replace join results in the synopsis upon update. We conduct extensive experiments using TPC-DS and a simulated road sensor data over several complex join queries and they demonstrate the clear advantage of SJoin over the best available baseline.