EIP-3300: Phase Out Refunds (#3300)

* wip phase out refunds

* update create date and eip number

* discussions-to

* rename file to eip#

* fix discussions-to url error from Travis

* Update EIPS/eip-3300.md

Co-authored-by: Micah Zoltu <micah@zoltu.net>

* Update EIPS/eip-3300.md

Co-authored-by: Micah Zoltu <micah@zoltu.net>

* Update EIPS/eip-3300.md

Co-authored-by: Micah Zoltu <micah@zoltu.net>

* Update EIPS/eip-3300.md

Co-authored-by: Micah Zoltu <micah@zoltu.net>

* Update EIPS/eip-3300.md

Co-authored-by: Micah Zoltu <micah@zoltu.net>

* Update EIPS/eip-3300.md

Co-authored-by: Micah Zoltu <micah@zoltu.net>

* Update EIPS/eip-3300.md

Co-authored-by: Micah Zoltu <micah@zoltu.net>

* Update EIPS/eip-3300.md

Co-authored-by: Micah Zoltu <micah@zoltu.net>

* initial clarification

* specify 1283 behavior

* specify negative refund removal

* start specifying activation costs and then simplify by disregarding them

* cleanup activation cost specifications

Co-authored-by: Micah Zoltu <micah@zoltu.net>

EIPS/eip-3300.md

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+---
+eip: 3300
+title: Phase out refunds
+author: William Morriss (@wjmelements)
+discussions-to: https://ethereum-magicians.org/t/eip-3300-phase-out-refunds/5434
+status: Draft
+type: Standards Track
+category: Core
+created: 2020-02-26
+---
+
+## Simple Summary
+Phases out the `SSTORE` and `SELFDESTRUCT` gas refunds.
+
+## Abstract
+This EIP would define a block when the `SSTORE` and `SELFDESTRUCT` refunds would begin to diminish.
+The refund would step linearly downward, eroding the implicit value of such refunds at an accelerating pace.
+
+## Motivation
+Refunds increase block elasticity, so the block gas target can exceed the number established by miners by up to 2x.
+This can cause hesitancy for miners to increase the block gas target.
+
+Refunds, tokenized or not, are valuable to their holders, especially during congestion.
+If refunds must be removed, a gradual change in their value would be less-disruptive to the gas market than sudden abolition.
+Refund consumption would proceed, especially during periods of congestion, and the refunds would be cleaned up from the state.
+Refund creation, driven by demand, would naturally diminish as the efficiency of the refunds fall.
+As the refund value approaches the activation cost, the implicit value of the refunds will approach zero, but in periods of congestion they will be cleaned up.
+
+This change is less work for the protocol developers than compensation and cleanup, while likely still achieving cleanup.
+
+
+## Specification
+Parameters:
+* `FORK_BLOCK_NUM`: EIP-3300 activation block
+* `REFUND_DECAY_STEP`: 1 gas
+* `REFUND_DECAY_FREQUENCY`: 100 blocks
+
+Computed:
+* `REFUND_DECAY`: `REFUND_DECAY_STEP * ceil((block.number + 1 - FORK_BLOCK_NUM) / REFUND_DECAY_FREQUENCY)`
+
+
+On the block this EIP activates, and again every `REFUND_DECAY_FREQUENCY` blocks, all gas refunds, including `SELFDESTRUCT` and `SSTORE` would diminish by `REFUND_DECAY_STEP`, until 0.
+The current difference is called the `REFUND_DECAY`, which shall be subtracted from each gas refund.
+
+For gas-cost regimes with refund removals that cancel prior refunds, the invariant that the refund counter cannot go negative will be preserved by diminishing the magnitude of those removals by `REFUND_DECAY`, until 0.
+
+
+### EIP-2929
+The refunds as of EIP-2929 are as follows:
+
+* 24000 for SELFDESTRUCT
+* `SSTORE_RESET_GAS - SLOAD_GAS` (5000 - 100)
+* `SSTORE_SET_GAS - SLOAD_GAS` (20000 - 100)
+* `SSTORE_SET_GAS - SLOAD_GAS` (20000 - 100)
+* `SSTORE_CLEARS_SCHEDULE` (15000)
+
+
+Each of these refunds would be decreased by the current `REFUND_DECAY`.
+
+There is also a case where `SSTORE_CLEARS_SCHEDULE` is removed from the refund counter.
+That removal will also diminish by `REFUND_DECAY_STEP` until 0, maintaining the non-negative refund counter invariant.
+
+
+## Rationale
+Persisted refunds would become worthless before they fall below their activation cost.
+Once the refunds are worthless, they can be removed by another hard fork without waiting for 0.
+The rate of diminishing specified would currently require (24000-5000) * 100 = 1,900,000 blocks for `SELFDESTRUCT` and (15000-5000) * 100 = 1,000,000 blocks for `SSTORE`.
+This timeframe is currently about a year, which should be enough flexibility for the remaining refunds to be consumed.
+
+
+## Backwards Compatibility
+This proposal breaks gas refunds, which contribute to block elasticity.
+The effect of this will be increased gas price volatility: higher highs and lower lows.
+
+Because the refund counter is separate from the gas counter, the block-to-block gas changes will not break `eth_estimateGas`.
+
+## Copyright
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).