OptChain: Optimal Transactions Placement for Scalable Blockchain Sharding

TL;DR

OptChain introduces a novel transaction placement method for sharded blockchains that significantly reduces cross-shard transactions, boosting throughput and decreasing confirmation times through an online graph-based approach.

Contribution

The paper presents OptChain, a new sharding paradigm that minimizes cross-shard transactions using an online graph method, improving performance and scalability.

Findings

Up to 10-fold reduction in cross-shard transactions

More than 2x decrease in confirmation time

50% increase in throughput

Abstract

A major challenge in blockchain sharding protocols is that more than 95% transactions are cross-shard. Not only those cross-shard transactions degrade the system throughput but also double the confirmation time, and exhaust an already scarce network bandwidth. Are cross-shard transactions imminent for sharding schemes? In this paper, we propose a new sharding paradigm, called OptChain, in which cross-shard transactions are minimized, resulting in almost twice faster confirmation time and throughput. By treating transactions as a stream of nodes in an online graph, OptChain utilizes a lightweight and on-the-fly transaction placement method to group both related and soon-related transactions into the same shards. At the same time, OptChain maintains a temporal balance among shards to guarantee the high parallelism. Our comprehensive and large-scale simulation using Oversim P2P library confirms a significant boost in performance with up to 10 folds reduction in cross-shard transactions, more than twice reduction in confirmation time, and 50% increase in throughput. When combined with Omniledger sharding protocol, OptChain delivers a 6000 transactions per second throughput with 10.5s confirmation time.