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.