Investigate allowing node to do post init before full sync is complete

[lrettig]

Right now, a user has to fully sync their node before they can do post init. They need to have seen all ATXs since genesis to validate them and discover a commitment ATX with a high weight as input for label generation. This isn't a big issue early on but will have severe UX consequences as the network ages and initial sync takes longer. We need to explore whether there's a way to avoid this requirement, or else to do some sort of "fast sync" of at least the chain of ATXs to allow a new smesher to do their post init quickly.

CC @noamnelke, @fasmat, @countvonzero

See (internal) slack thread

the primary reason is outlined here: https://community.spacemesh.io/t/possible-dos-against-pops-vrf-beacon-and-mitigation/210

[countvonzero]

the title is misleading. full sync is not the same as ATX synced. sync flow fetches ATX befpre everything else

[fasmat]

I think we can close this issue, since we know the reasons as to why the node behaves as it does at the moment. In summary:

• PoST initialization can start immediately, smapp does not need to wait for a full sync to start Smeshing
• PoST initialization progress will be stuck at 0% for some time because the node needs to fetch and validate a recent ATX (plus at least of of it's history) - this is not a full sync and already prioritised over synching other data by the node.
  • Future work item "Improve PoST progress feedback": at the moment the stream that returns the progress state of PoST initialization only returns how many labels have been written. Instead it should return "Phase 1" and "Phase 2 progress", where "Phase 1" is the estimated progress on ATX validation and "Phase 2" the progress on label creation. This allows for a better UX on Smapp
  • Future work item "PoST Quick sync": a node that receives an ATX from the current epoch should just optimistically assume that this ATX is valid and start initializing with it while it is also validating ATXs in the background. Should the ATX turn out to be invalid the PoST initialization has to restart with an ATX that was determined to be valid. This way "Phase 2" can start immediately but might need to revert once if the initially picked ATX turns out to be invalid.

[lrettig]

@fasmat I think it might be helpful to keep this open as an "epic" task tracking the to do items you listed. (There's another to do item for smapp: allow smeshing to be configured immediately rather than requiring the user to wait for sync to complete.)