Worst-case Optimal Binary Join Algorithms under General $\ell_p$ Constraints

TL;DR

This paper introduces a simple, worst-case optimal join algorithm for relations with arity at most two under general $\, ext{l}_p$-norm size bounds, extending prior work beyond size and degree bounds.

Contribution

It presents a novel join algorithm that is optimal under $\, ext{l}_p$-norm bounds for $p \,\in\ (1,2]$, and addresses open questions from previous research.

Findings

Algorithm is simple and p-independent.

Achieves worst-case optimality for $p\in(1,2]$ and large girth graphs.

Avoids poly-log factors of previous algorithms.

Abstract

Worst-case optimal join algorithms have so far been studied in two broad contexts -- $(1)$ when we are given input relation sizes [Atserias et al., FOCS 2008, Ngo et al., PODS 2012, Velduizhen et. al, ICDT 2014] $(2)$ when in addition to size, we are given a degree bound on the relation [Abo Khamis et al., PODS 2017]. To the best of our knowledge, this problem has not been studied beyond these two statistics even for the case when input relations have arity (at most) two. In this paper, we present a worst-case optimal join algorithm when are given $\ell_{p}$-norm size bounds on input relations of arity at most two for $p \in (1, 2]$. ($p=1$ corresponds to relation size bounds and $p=\infty$ corresponds to the degree bounds.) The worst-case optimality holds any fixed $p \in (2, \infty)$ as well (as long as the join query graph has large enough girth). Our algorithm is {\em simple}, does not depend on $p$ (or) the $\ell_{p}$-norm bounds and avoids the (large) poly-log factor associated with the best known algorithm PANDA [Abo Khamis et al., PODS 2017] for the size and degree bounds setting of the problem. In this process, we (partially) resolve two open question from [Ngo, 2018 Gems of PODS]. We believe our algorithm has the {\em potential} to pave the way for practical worst-case optimal join algorithms beyond the case of size bounds.