Towards Reconfigurable Linearizable Reads

Abstract

Linearizable datastores are desirable because they provide users with the illusion that the datastore is run on a single machine that performs client operations one at a time. To reduce the performance cost of providing this illusion, many specialized algorithms for linearizable reads have been proposed which significantly improve read performance compared to write performance. The main difference between these specialized algorithms is their performance under different workloads. Unfortunately, since a datastore's workload is often unknown or changes over time and system designers must decide on a single read algorithm to implement ahead of time, a datastore's performance is often suboptimal as it cannot adapt to workload changes. In this paper, we lay the groundwork for addressing this problem by proposing Chameleon, an algorithm for linearizable reads that provides a principled approach for datastores to switch between existing read algorithms at runtime. The key observation that enables this generalization is that all existing algorithms are specific read-write quorum systems. Chameleon constructs a generic read-write quorum system, by using tokens that are included to complete write and read operations. This token quorum system enables Chameleon to mimic existing read algorithms and switch between them by transferring these tokens between processes.