Add missing comment on why last_update_message is None

diff --git a/lightning/src/routing/network_graph.rs b/lightning/src/routing/network_graph.rs
index dd6d7d7ed734aadbd7f89f93308aefd0223a9f79..b454216b48ca091ac04e0656aee4e47c604e3f44 100644 (file)
--- a/lightning/src/routing/network_graph.rs
+++ b/lightning/src/routing/network_graph.rs
@@ -217,6 +217,9 @@ pub struct DirectionalChannelInfo {
        /// Fees charged when the channel is used for routing
        pub fees: RoutingFees,
        /// Most recent update for the channel received from the network
+       /// Mostly redundant with the data we store in fields explicitly.
+       /// Everything else is useful only for sending out for initial routing sync.
+       /// Not stored if contains excess data to prevent DoS.
        pub last_update_message: Option<msgs::ChannelUpdate>,
 }