Many classical blockchains are known to have an embarrassingly low transaction throughput, down to Bitcoin's notorious seven transactions per second limit.Various proposals and implementations for increasing throughput emerged in the first decade of blockchain research. But how much concurrency is possible? In their early days, blockchains were mostly used for simple transfers from user to user. More recently, however, decentralized finance (DeFi) and NFT marketplaces have completely changed what is happening on blockchains. Both are built using smart contracts and have gained significant popularity. Transactions on DeFi and NFT marketplaces often interact with the same smart contracts. We believe this development has transformed blockchain usage. In our work, we perform a historical analysis of Ethereum's transaction graph. We study how much interaction between transactions there was historically and how much there is now. We find that the rise of DeFi and NFT marketplaces has led to an increase in "centralization" in the transaction graph. More transactions are now interconnected: currently there are around 200 transactions per block with 4000 interdependencies between them. We further find that the parallelizability of Ethereum's current interconnected transaction workload is limited. A speedup exceeding a factor of five is currently unrealistic.

翻译：许多经典区块链以极低的交易吞吐量闻名，最典型的是比特币饱受诟病的每秒七笔交易限制。在区块链研究的第一个十年中，业界提出了多种提升吞吐量的方案与实现。然而，究竟能达到多大的并发性？早期区块链主要用于用户间的简单转账。但近年来，去中心化金融（DeFi）和NFT市场彻底改变了区块链上的活动形态。两者均基于智能合约构建，并已获得广泛流行。DeFi和NFT市场的交易往往与相同的智能合约交互。我们认为这一发展已彻底改变了区块链的用途。在本研究中，我们对以太坊的交易图谱进行了历史分析，考察了交易间互动的历史水平与当前现状。研究发现，DeFi和NFT市场的兴起导致交易图谱出现"中心化"趋势：更多交易相互关联——当前每个区块约包含200笔交易，其间存在约4000条相互依赖关系。我们进一步发现，以太坊当前相互关联的交易工作负载的并行化能力有限，目前实现超过五倍的加速效果并不现实。