Add FLIP 204 - Smart-Contract-Specified Epoch Switchover Timing

[jordanschalm]

Adds FLIP 204

[turbolent]

Only looked at the Cadence code

[joshuahannan]

Looks pretty good to me! I am also in favor of option 2. Shouldn't be too hard to implement

[joshuahannan]

How is the reference epoch chosen?

[jordanschalm]

It doesn't really matter. We can pick any previous epoch transition. Initially we would just pick the most recent one.

The same reference epoch can be used for as long as we want, so long as there is no discontinuity in epoch timing (very long period of downtime or epoch fallback mode being active for an extended period). If that happens, then we would pick a new reference epoch (the first one after the discontinuity).

[joshuahannan]

If we're using a reference epoch to calculate the time of future epochs and the reset epoch doesn't happen at the expected epoch switchover time, won't that be a problem since it wasn't the expected length?

[jordanschalm]

No, I don't think it would cause a problem. Using a reference epoch decouples the target end time computation from actual switchover timing. The target end time is 100% dependent on that reference epoch; the actual network can do anything in the interim and it won't affect the target end time.

That can be a downside, if we have a large, durable timing change, because it won't be reflected here. We would need to manually change the reference epoch to accommodate that. But we don't expect that to happen, so don't optimize for it.

It can be an upside, because:

• we can do the resetEpoch at any time - it has no impact
• small fluctuations in switchover timing have no impact and therefore don't accumulate

[joshuahannan]

okay I think that makes sense

[joshuahannan]

@jordanschalm Would you want to work on the implementation and make a PR based off onflow/flow-core-contracts#379 so we can try to get this into the same upgrade as the other changes? I addressed all your comments so it is good to go from my end

[jordanschalm]

Yes, although I will not have bandwidth to work on this until after the Offsite next week - Oct 16 at the earliest. Is there a timeline for doing that upgrade?

[joshuahannan]

That should probably be fine. We don't have a timeline yet