# SSS: Scalable Key-Value Store with External Consistent and Abort-free Read-only Transactions

## TL;DR

SSS is a scalable distributed key-value store that guarantees external consistency and never aborts read-only transactions, using vector clocks and snapshot-queuing without centralized synchronization.

## Contribution

The paper introduces SSS, a novel distributed concurrency control technique combining vector clocks and snapshot-queuing to achieve external consistency without centralized synchronization.

## Key findings

- SSS outperforms 2PC baseline by up to 7x with 20 nodes.
- SSS outperforms ROCOCO by up to 2.2x with long read-only transactions.
- SSS provides external consistency and abort-free read-only transactions in a scalable manner.

## Abstract

We present SSS, a scalable transactional key-value store deploying a novel distributed concurrency control that provides external consistency for all transactions, never aborts read-only transactions due to concurrency, all without specialized hardware. SSS ensures the above properties without any centralized source of synchronization. SSS's concurrency control uses a combination of vector clocks and a new technique, called snapshot-queuing, to establish a single transaction serialization order that matches the order of transaction completion observed by clients. We compare SSS against high performance key-value stores, Walter, ROCOCO, and a two-phase commit baseline. SSS outperforms 2PC-baseline by as much as 7x using 20 nodes; and ROCOCO by as much as 2.2x with long read-only transactions using 15 nodes.