Assuming a graph size of 50,000 channels, an interval of 20 minutes
would cause nodes to consume about 600MB per month in bandwidth doing
these routine historical sync spot checks. In this commit, we increase
to one hour, which consumes about 300MB per month.
This commit reduces the number of channels a syncer will request from
the remote node in a single QueryShortChanIDs message. The current size
is derived from the chunkSize, which is meant to signal the maximum
number of short chan ids that can fit in a single ReplyChannelRange
message. For EncodingSortedPlain, this number is 8000, and we use the
same number to dictate the size of the batch from the remote peer.
We modify this by introducing a separately configurable batchSize, so
that both can be tuned independently. The value is chosen to reduce the
amount of buffering the remote party will perform, only requiring them
queue 500 responses, as opposed to 8000. In turn, this reduces larges
spikes in allocation on the remote node at the expense of a few extra
round trips for the control messages. However, will be negligible since
the control messages are much smaller than the messages being returned.
In this commit, we address a bug where we'd attempt to replace the
stale active syncer when it transitioned to a passive syncer. This
replacement logic is only intended to happen when the active syncer
disconnects, as rotateActiveSyncerCandidate chooses and queues its own
replacement.
In this commit, we introduce a new subsystem for the gossiper: the
SyncManager. This subsystem is a major overhaul on the way the daemon
performs the graph query sync state machine with peers.
Along with this subsystem, we also introduce the concept of an active
syncer. An active syncer is simply a GossipSyncer currently operating
under an ActiveSync sync type. Before this commit, all GossipSyncer's
would act as active syncers, which means that we were receiving new
graph updates from all of them. This isn't necessary, as it greatly
increases bandwidth usage as the network grows. The SyncManager changes
this by requiring a specific number of active syncers. Once we reach
this specified number, any future peers will have a GossipSyncer with a
PassiveSync sync type.
It is responsible for three main things:
1. Choosing different peers randomly to receive graph updates from to
ensure we don't only receive them from the same set of peers.
2. Choosing different peers to force a historical sync with to ensure we
have as much of the public network as possible. The first syncer
registered with the manager will also attempt a historical sync.
3. Managing an in-order queue of active syncers where the next cannot be
started until the current one has completed its state machine to ensure
they don't overlap and request the same set of channels, which
significantly reduces bandwidth usage and addresses a number of issues.
