Graphical Join: A New Physical Join Algorithm for RDBMSs

TL;DR

The paper introduces Graphical Join, a novel physical join algorithm for RDBMSs that significantly improves performance and space efficiency for complex join operations by leveraging probabilistic graphical models and inference algorithms.

Contribution

It presents a new join algorithm, Graphical Join, which maps join processing to probabilistic graphical models and demonstrates substantial performance and space savings over existing methods.

Findings

Up to 820X faster join computation on disk compared to competitors.

Performance improvements up to 64X in-memory and 820X on disk.

Space requirements are up to 78,750X smaller than existing systems.

Abstract

Join operations (especially n-way, many-to-many joins) are known to be time- and resource-consuming. At large scales, with respect to table and join-result sizes, current state of the art approaches (including both binary-join plans which use Nested-loop/Hash/Sort-merge Join algorithms or, alternatively, worst-case optimal join algorithms (WOJAs)), may even fail to produce any answer given reasonable resource and time constraints. In this work, we introduce a new approach for n-way equi-join processing, the Graphical Join (GJ). The key idea is two-fold: First, to map the physical join computation problem to PGMs and introduce tweaked inference algorithms which can compute a Run-Length Encoding (RLE) based join-result summary, entailing all statistics necessary to materialize the join result. Second, and most importantly, to show that a join algorithm, like GJ, which produces the above join-result summary and then desummarizes it, can introduce large performance benefits in time and space. Comprehensive experimentation is undertaken with join queries from the JOB, TPCDS, and lastFM datasets, comparing GJ against PostgresQL and MonetDB and a state of the art WOJA implemented within the Umbra system. The results for in-memory join computation show performance improvements up to 64X, 388X, and 6X faster than PostgreSQL, MonetDB and Umbra, respectively. For on-disk join computation, GJ is faster than PostgreSQL, MonetDB and Umbra by up to 820X, 717X and 165X, respectively. Furthermore, GJ space needs are up to 21,488X, 38,333X, and 78,750X smaller than PostgresQL, MonetDB, and Umbra, respectively.