MultiChannel and MultiPTLC: Towards A Global High-Availability CP Database For Bitcoin Payments

The CAP Theorem elucidates a fundamental principle in distributed computing, asserting that it is impossible for a distributed data store to simultaneously ensure consistency, availability, and partition tolerance. This theorem underpins the design of many databases, including those used for financial transactions like Bitcoin. However, due to the inherent unreliability of networks, practical systems often have to choose between being consistent and partition-tolerant (CP) or available and partition-tolerant (AP). The Bitcoin blockchain operates as an AP database, prioritizing availability and partition tolerance over consistency. This design choice supports the blockchain's robustness against downtime but introduces potential temporary inconsistencies, such as the possibility of reverting zero-confirmation transactions.

The Lightning Network represents a significant evolution in this landscape, functioning as a global CP database built atop Bitcoin's underlying AP architecture. The network achieves consistency and partition tolerance through two key mechanisms: channels and Hashed Timelock Contracts (HTLCs). Channels allow for local, two-node CP databases that can securely hold funds and update their state with high consistency. HTLCs extend this local consistency to a global scale by ensuring atomic updates across multiple financial databases, thus enabling fast and reliable financial transactions without the need for traditional block confirmation times.

However, the Lightning Network faces challenges regarding availability. Specifically, its reliance on two-node channels means that if one node goes offline, it disrupts the channel's ability to update its state, thereby lowering the network's overall availability. To address this, a novel approach involving multi-signature schemes and more complex contractual arrangements, such as 2-of-2 multisigs combined with a 2-of-3 scheme among forwarding nodes, has been proposed. This setup aims to balance the need for high availability with the principles of self-custody inherent in cryptocurrency philosophy.

Furthermore, the introduction of Point Time-Locked Contracts (PTLCs) offers a promising enhancement over HTLCs by facilitating stuckless payments—allowing for multiple payment attempts with only one ultimately claimable by the receiver. This mechanism reduces liquidity requirements for end-users and potentially increases the success rate of payments through the network.

In summary, while the Bitcoin blockchain itself functions as an AP database conducive to high availability but susceptible to temporary inconsistencies, the Lightning Network offers a shift towards a CP model, prioritizing consistency and partition tolerance. This shift is significant for financial applications requiring immediate and reliable transaction settlement. However, achieving a high-availability CP database in this context necessitates innovative solutions to reconcile the tension between availability, consistency, and the non-negotiable aspect of self-custody in digital asset management.