Path Queries: Addressing Payment Reliability and Routing limitations

The email delves into a critical evaluation of a proposal aimed at enhancing the efficiency of routing payments in the Lightning Network by comparing it with an alternative approach that involves sharing liquidity information within the local neighborhood, as detailed in a GitHub pull request. The sender acknowledges the potential benefits of cascading path queries for improved payment routing but raises concerns about the practical implications, such as the possibility of probing the entire network, leading to significant communication overhead due to the dynamic nature of liquidity states.

The discussion extends to the limitations inherent in the network's liquidity and how these impact payment feasibility. Despite the proposition that full knowledge of liquidity could theoretically improve routing decisions, the sender references studies, including one which indicates that 2.5% of all payments cannot exceed 766 sats regardless of liquidity certainty (study link). This bottleneck is largely attributed to the outbound liquidity of the sender and the inbound liquidity of the recipient, suggesting that removing uncertainty around liquidity will not necessarily lead to larger feasible payments or lower fees.

Moreover, the sender critiques the claimed benefits of the proposal, such as eliminating the need for a fully synced channel graph, enabling more dynamic routing policies, distributing routing more evenly, and facilitating network growth. They argue that while these benefits sound promising, they may not materialize as expected due to various factors like the potential for increased fees from routing nodes capitalizing on their desirable liquidity and the quick depletion of channels due to more informed routing decisions.

In conclusion, while the sender appreciates the elegance and cleaner approach of the proposed idea compared to existing methods like trampoline routing, there is skepticism regarding its ability to significantly enhance the reliability and efficiency of the Lightning Network. The sender suggests considering a simple flag in channel updates to indicate liquidity positioning as a potentially more effective solution for reducing uncertainty in liquidity, promoting further discussion and comparison of ideas within the community to advance the network's capabilities.