What if we tried Less Power? -- Lessons from studying the power of choices in hashing-based data structures

TL;DR

This paper reviews the impact of the number of choices in hashing-based data structures, highlighting that more choices often add costs outweighing benefits, and introduces a new data structure leveraging coarse-grained choices.

Contribution

It provides a comprehensive survey on the power of choices in hashing and proposes a novel data structure using coarse-grained choices at a higher level.

Findings

More than two choices often incur higher costs than benefits

A new data structure uses $1+ ext{epsilon}$ choices at a coarser granularity

Coarse-grained choices can be effective in space-efficient data structures

Abstract

In the first part of this survey, we review how the power of two choices underlies space-efficient data structures like cuckoo hash tables. We'll find that the additional power afforded by more than 2 choices is often outweighed by the additional costs they bring. In the second part, we present a data structure where choices play a role at coarser than per-element granularity. In some sense, we rely on the power of $1+\epsilon$ choices.