Memoryless Worker-Task Assignment with Polylogarithmic Switching Cost

TL;DR

This paper introduces a novel approach to memoryless worker-task assignment with polylogarithmic switching cost, providing both probabilistic and explicit constructions, and explores its implications for metric embeddings.

Contribution

It presents the first polylogarithmic upper bounds for switching cost and establishes a super-constant lower bound, advancing understanding of dynamic assignment problems.

Findings

Achieves $O( ext{log } w ext{ log } (wt))$ switching cost via probabilistic method

Provides an explicit construction with polylogarithmic switching cost

Shows existence of task sets where optimal switching cost equals $w$

Abstract

We study the basic problem of assigning memoryless workers to tasks with dynamically changing demands. Given a set of $w$ workers and a multiset $T \subseteq[t]$ of $|T|=w$ tasks, a memoryless worker-task assignment function is any function $\phi$ that assigns the workers $[w]$ to the tasks $T$ based only on the current value of $T$. The assignment function $\phi$ is said to have switching cost at most $k$ if, for every task multiset $T$, changing the contents of $T$ by one task changes $\phi(T)$ by at most $k$ worker assignments. The goal of memoryless worker task assignment is to construct an assignment function with the smallest possible switching cost. In past work, the problem of determining the optimal switching cost has been posed as an open question. There are no known sub-linear upper bounds, and after considerable effort, the best known lower bound remains 4 (ICALP 2020). We show that it is possible to achieve polylogarithmic switching cost. We give a construction via the probabilistic method that achieves switching cost $O(\log w \log (wt))$ and an explicit construction that achieves switching cost $\operatorname{polylog} (wt)$. We also prove a super-constant lower bound on switching cost: we show that for any value of $w$, there exists a value of $t$ for which the optimal switching cost is $w$. Thus it is not possible to achieve a switching cost that is sublinear strictly as a function of $w$. Finally, we present an application of the worker-task assignment problem to a metric embeddings problem. In particular, we use our results to give the first low-distortion embedding from sparse binary vectors into low-dimensional Hamming space.