Increase the default outgoing bandwidth

[yyforyongyu]

When replying to gossip_timestamp_filter, we will send ChannelAnnouncement, NodeAnnouncement and two ChannelUpdate1s. And their sizes are,

• ChannelAnnouncement1: This message has a mostly fixed size.

  • Fixed size fields: 428 bytes (signatures, chain hash, short channel ID, node IDs, and bitcoin keys).
  • Variable size fields: A feature vector (minimum 2 bytes) and extra opaque data.
  • Minimum payload size: 430 bytes

• NodeAnnouncement: This message has both fixed and variable size components.

  • Fixed size fields: 136 bytes (signature, timestamp, node ID, color, and alias).
  • Variable size fields: A feature vector (minimum 2 bytes) and a list of network addresses (minimum 2 bytes for an empty list).
  • Minimum payload size: 140 bytes

• ChannelUpdate1: This message has a mostly fixed size.

  • Fixed size fields: 128 bytes (signature, chain hash, short channel ID, timestamp, flags, fee information, and HtlcMaximumMsat).
  • Minimum payload size: 136 bytes

Best case: Assuming the minimal sizes, we will send 430+140+136*2 = 842 bytes per channel, with the current default of 100kb, we can process 121 channels per second.

Worst case: Assuming max size, when all the msgs are using extra bytes, we will send 65535*4 = 262,140 bytes per channel, and with the current default, we can process 6 channels per second. But this is highly unlikely.

Note that this value is shared among all peers, which means if we have 10 peers, we can only process 12 channels per peer per second.

[gemini-code-assist]

Summary of Changes

Hello @yyforyongyu, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly increases the default outgoing gossip bandwidth limits within the system. The primary goal is to improve the efficiency and speed at which the node can propagate critical network information, such as channel and node announcements, especially when responding to gossip requests. This change aims to alleviate potential bottlenecks in network synchronization and message dissemination.

Highlights

• Increased Outgoing Gossip Bandwidth: The default values for DefaultMsgBytesBurst and DefaultMsgBytesPerSecond have been increased tenfold, from 100KB/s to 1MB/s for the rate, and from 200KB to 2MB for the burst. This significantly boosts the capacity for sending gossip messages.
• Improved Configuration Documentation: The descriptions for the MsgRateBytes and MsgBurstBytes configuration options in lncfg/gossip.go and sample-lnd.conf have been updated to provide clearer and more detailed explanations of their purpose and interaction within the token bucket rate-limiting scheme.

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[gemini-code-assist]

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[Roasbeef]

Why do we need to also increase this?

[yyforyongyu]

the burst must be greater than the msg-rate-bytes otherwise msg-rate-bytes may not take effect, more details here.

[morehouse]

I think 1 MB/s is a reasonable default outgoing rate limit. At least in the US, typical upload speeds are higher than this.

Lower-end setups may want to rate limit more aggressively.

[Roasbeef]

LGTM 🏊‍♀️