FIP Discussion: Correct Quality Calculation on Expiration

[kaitlin-beegle]

[Adding issue as a placeholder for community discussion on behalf of FIP authors]

Simple Summary

Sector quality is defined as a spacetime average of the quality of the deals stored in the sector. The current protocol implementation does not work as expected when sectors are extended because deal spacetime is overcounted. This leads to minor incentive issues. This FIP fixes the discrepancy.

Abstract

DealWeight and VerifiedDealWeight in a sector's past is no longer included in the quality calculation for the extended sector. Instead the past spacetime of the sectors is "spent" and only the remaining deal spacetime of the sector's original life is counted.

To avoid extending the market actor interface for a small change this FIP proposes getting an approximate value for the remaining spacetime of deals and verified deals. A good approximation is to multiply deal weight by the fraction of sector lifetime remaining.

(See link to full FIP draft here.)

CC FIP authors: @Stebalien, @ZX, @ZenGround0

[ZenGround0]

The title of this issue indicates the wrong fip. It should be "Correct quality calculation on expiration" instead of the "Add return value to WithdrawBalance"

[kaitlin-beegle]

@ZenGround0 good catch; copy+pasted from the wrong FIP. Updated!

[xinaxu]

The verified deal requries 10x initial pledge. (See https://spec.filecoin.io/#section-systems.filecoin_mining.miner_collaterals.initial-pledge-collateral).
Now with correct quality calculation on/after expiration, will the excessive initial pledge collateral be returned and if so how

[ZenGround0]

This FIP does not add any new features to sector extension recalculating IP. IP remains unchanged before and after extension as is the case now for all sectors. Since the verified deals in the sector should all be finished by the first expiration if pledge is constraining onboarding then it seems that a good strategy is to let these sectors expire without extension and seal a new CC sector with lower pledge instead.

FYI @zixuanzh

[kaitlin-beegle]

Closing due to FIP acceptance!