DAG-Sword: A Simulator for DAG-Oriented Proof-of-Work Blockchains with Realistic Network Topologies

Interesting blockchain properties have received considerable attention in research and practical applications. However, some properties, such as the transaction throughput, remained limited, especially in Proof-of-Work blockchains. Therefore, several promising directions, such as DAG-based protocols, emerged to respond to the throughput bottleneck. In this paper, we present a discrete-event simulator of DAG-based consensus protocols. Our simulator can simulate realistic blockchain networks created from data collected from a Bitcoin network, while its network configuration can be customized. The simulated network consists of honest and malicious miners. Malicious miners do not make any attack on consensus but they use a different than honest (random) transaction selection strategy to include transactions in the block to earn more profits than honest miners. This harms the performance of some DAG-based protocols, such as PHANTOM and GHOSTDAG, and thus decreases the overall throughput, which we demonstrate in our experiments and confirm the results of the related work achieved on a small network of 10 nodes. Next, we empirically compare different algorithms implementing the random transaction selection strategy from the mempool structure, and we propose a composite mempool structure that is memory-efficient and thus convenient for simulations of various transaction selection strategies over large-scale realistic networks.