Etna: a Fault-tolerant Algorithm for Atomic Mutable DHT Data

Abstract

This paper presents Etna, an algorithm for atomic reads and writes of replicated data stored in a distributed hash table. Etna correctly handles dynamically changing sets of replica hosts, and is optimized for reads, writes, and reconfiguration, in that order.Etna maintains a series of replica configurations as nodes in the system change, using new sets of replicas from the pool supplied by the distributed hash table system. It uses the Paxos protocol to ensure consensus on the members of each new configuration. For simplicity and performance, Etna serializes all reads and writes through a primary during the lifetime of each configuration. As a result, Etna completes read and write operations in only a single round from the primary.Experiments in an environment with high network delaysshow that Etna's read latency is determined by round-tripdelay in the underlying network, while write and reconfiguration latency is determined by the transmission time required to send data to each replica. Etna's write latency is about the same as that of a non-atomic replicating DHT, and Etna's read latency is about twice that of a non-atomic DHT due to Etna assembling a quorum for every read.