Prediction-based UTXO Cache Optimization for Bitcoin Lightweight Full Nodes

Since version 0.11 of Bitcoin Core, a user can run a full node in pruning mode, i.e. a pruned node, in resource-limited devices. The pruned node is a lightweight full node as it can independently verify new transactions and blocks received from other peers in the Bitcoin network by only maintaining some recently verified blocks (not the complete blockchain) and the complete Unspent Transaction Output (UTXO) set. However, the rapid increase in the size of the UTXO set has caused the main part of the UTXO set to be stored in the low-speed disk, and thus slows down the verification speed of new blocks in lightweight full nodes. Existing verification schemes for pruned nodes do not take advantage of the fact that different UTXO-related transactions are included in a new block with different probabilities, resulting in poor verification performance. In this paper, we propose a prediction-based UTXO cache optimization mechanism to increase the verification speed of new blocks. In order to achieve higher prediction accuracy and reduce the memory requirements of UTXO set, we first design a method to synchronize unconfirmed transactions for lightweight full nodes to ensure that the local and miners' unconfirmed transaction sets are highly consistent. Then, a lightweight full node predicts which unconfirmed transactions will have a greater probability of appearing in the new block by utilizing the fact that most miners will prioritize unconfirmed transactions to maximize the total transaction fee when mining a new block. Based on this mechanism, we can pre-load the UTXOs required for new block verification into the memory, thereby greatly improving the verification performance. Experimental results show that the proposed mechanism can accelerate the block verification of lightweight full nodes with small memory requirements.