# The Impact of RDMA on Agreement

## TL;DR

This paper demonstrates that RDMA technology enables new consensus algorithms that achieve high resilience and performance simultaneously, surpassing traditional trade-offs in distributed systems.

## Contribution

It introduces novel consensus algorithms leveraging RDMA, reducing process requirements and decision delays while tolerating memory failures.

## Key findings

- RDMA enables high-resilience, high-performance consensus algorithms.
- Algorithms decide in two network delays under various failure models.
- Memory failures are tolerated without compromising safety.

## Abstract

Remote Direct Memory Access (RDMA) is becoming widely available in data centers. This technology allows a process to directly read and write the memory of a remote host, with a mechanism to control access permissions. In this paper, we study the fundamental power of these capabilities. We consider the well-known problem of achieving consensus despite failures, and find that RDMA can improve the inherent trade-off in distributed computing between failure resilience and performance. Specifically, we show that RDMA allows algorithms that simultaneously achieve high resilience and high performance, while traditional algorithms had to choose one or another. With Byzantine failures, we give an algorithm that only requires $n \geq 2f_P + 1$ processes (where $f_P$ is the maximum number of faulty processes) and decides in two (network) delays in common executions. With crash failures, we give an algorithm that only requires $n \geq f_P + 1$ processes and also decides in two delays. Both algorithms tolerate a minority of memory failures inherent to RDMA, and they provide safety in asynchronous systems and liveness with standard additional assumptions.