Binary Fuse filters as an alternative to BIP 158 GCS

The ongoing development and optimization of compact block filter clients present significant challenges and opportunities for wallet developers. Compact block filters serve as block-based sources of information that keep growing linearly over time, regardless of whether the user actively engages with their wallet. This necessitates a structured approach to data synchronization to manage the increasing data without overwhelming the user’s device resources. It is suggested that wallet developers implement a weekly background sync protocol, ideally executed when the user's device is connected to both battery and wifi. This method ensures data updates are processed regularly without requiring active user participation.

During such synchronizations, even if there is no immediate expectation of a transaction by the user, it remains critical to verify each block for potential transactions involving predefined scripts. The use of a low-bandwidth filter with a higher rate of false positives offers a strategic advantage. It allows app developers to determine whether a detailed check of the block range is unnecessary upon the next app opening or if there is a need to download specific filters during startup. The balance between minimizing the size of these filters and maintaining sufficient accuracy is crucial; smaller filters are less likely to be interrupted by operating systems due to excessive running times or bandwidth usage.

Pieter Wuille provides insights on optimizing Golomb-Coded Set (GCS) filters to achieve desired false positive rates in his great post. Utilizing these principles, an analysis was conducted to estimate the potential index sizes for blocks ranging from 480,000 to 940,000 with varying parameters. The results illustrate a scale of index sizes from approximately 5.89 GB to 10.29 GB, depending on the specificity and accuracy required by the filter settings. These findings underline the feasibility of developing a "bandwidth limited" GCS filter tailored for users who only need to query a limited number of scripts, thereby conserving bandwidth and enhancing performance. For those interested in the technical details or considering similar analyses, the script used for computing these index sizes is accessible on GitHub here.

This approach not only optimizes data management within digital wallets but also aligns with user expectations and technical constraints, paving the way for more efficient and user-friendly wallet applications.