delvingbitcoin

Quick peer gossip catchup protocol

Quick peer gossip catchup protocol

Original Postby cdecker

Posted on: December 6, 2023 13:23 UTC

The concept of efficiently synchronizing with client nodes in a network is achieved through lnsync, which implements an arbitrary ordering system that the serving node applies to messages.

This ordering facilitates clients' ability to seek through messages for synchronization purposes. The advantage of such a system lies in its simplicity and backward compatibility, allowing for some level of misordering without significant consequences as it may only result in slightly more data than necessary being transmitted.

Messages in the network are sorted based on different criteria to facilitate this process. For instance, channel_update and node_announcement messages are sorted by their timestamps, enabling clients to query a specific range of these timestamps. However, channel_announcement messages present a unique challenge as they lack timestamps, making it difficult to order them uniquely among other related messages. To address this quandary, it is proposed that channel_announcement should be included whenever a querying node requests a timestamp range that includes any update to the channel, regardless of the lack of a unique ordering position for these announcements.

A key benefit of this approach is the elimination of the need for per-peer storage, simplifying the startup process. Upon startup, nodes calculate an operational timestamp by loading the last known online timestamp, subtracting a predefined buffer (suggested as half an hour), and then communicating this timestamp during reconnection. As a result, nodes do not have to store information for each peer individually but instead maintain a single timestamp up to which they consider themselves updated. They can then request incremental updates from peers based on this timestamp, enhancing efficiency in keeping the network synchronized.