Periodic packet clearing functionality (clear_interval) in Hermes v1

[adizere]

Note: this came up from a Hermes user in Discord. I'm putting the question and answer here since they might come up again.

Question

Why does hermes only start periodic packets clearing for a channel (related to clear_interval) only from the moment when a ibc event is seen for this channel ? Example:

• Hermes start. No periodic packets clearing (no logs)
• An IBC tx is made, so hermes sees events like SendPackets.
• Hermes handle packets relaying.
• Periodic packets clearing starts for the related channel.

Answer

This is an assumption we made in the relayer architecture, essentially. The assumption is as follows: For as long as Hermes does not observe any WebSocket events for a certain channel X, then there is no activity on that channel, hence no reason to spawn the worker for relaying packets on X, so no need to do packet clearing.

If at relayer init time there are un-relayed packets on X and clear_on_start = true, then the relayer spawns the worker for X; otherwise, the worker for X only starts when there is WebSocket event activity. Once the worker is spawned, it will periodically do packet clearing every clear_interval blocks.