diff --git a/EIPS/eip-2035.md b/EIPS/eip-2035.md new file mode 100644 index 00000000..6b0eac7f --- /dev/null +++ b/EIPS/eip-2035.md @@ -0,0 +1,81 @@ +--- +eip: 2035 +title: Stateless Clients - Repricing SLOAD and SSTORE to pay for block proofs +author: Alexey Akhunov (@AlexeyAkhunov) +discussions-to: https://ethereum-magicians.org/t/eip-2035-stateless-clients-repricing-sload-and-sstore-to-pay-for-block-proofs/3284 +status: Draft +type: Standards Track +category: Core +created: 2019-05-16 +--- + + + +## Simple Summary + +The gas cost of EVM opcodes `SLOAD` and `SSTORE` increases in order to accommodate extra bandwidth required to propagate block proof together with the block +headers and block bodies, as explained [here](https://medium.com/@akhounov/data-from-the-ethereum-stateless-prototype-8c69479c8abc). + +## Abstract + +It is part of the State Rent roadmap. This particular change prepares Ethereum for introduction of the block proofs (current understanding is that they +can be introuced without a hard fork). The introduction of the block proofs allows any Ethereum node that wishes to receive them, to process transactions +in the blocks without needing to access the Ethereum state. All necessary information for the execution (and the proof of validity) is continued in the +block proofs. In most Ethereum nodes, it will speed up the block processing and reduce the memory footprint of such processing. For mining nodes, however, +there will be more work to do to construct and transmit the block proofs. Therefore, the extra charge (payable to the miners) is introduced. In the first +phase, only contract storage will be covered by the block proofs. It means that the Ethereum nodes will still need access to the accounts in the state, +but block proofs will make it optional to have access to contract storage for executing transactions. Therefore, only `SSTORE` and `SLOAD` opcodes are +affected. + +## Motivation + +There is [empirical analysis](https://github.com/holiman/vmstats/blob/master/README.md) showing that `SLOAD` opcode is currently underpriced in terms +of execution latency it adds to the block processing. The hypothesis is that it is due to the latency of the database accesses. In the same +analysis, `SSTORE` is not considered, because its effect on the database accesses can be (and are in many implementations) delayed until the end of +the block. Stateless clients approach to the contract storage will largely negate that latency because no database accesses will be required. +Instead, bandwidth consumption goes up. There is emprical analysis (unpublished, but will be) suggesting that 1 uncached `SSTORE` or `SLOAD` adds +at most 1 kB to the block proofs. At the current cost of data transmission (68 gas per byte), this translates to the increase of gas cost of both +operations by 69k gas. However, in light of proposal in [EIP-2028](https://eips.ethereum.org/EIPS/eip-2028), the increase can be made much smaller. + +## Specification + +Not very formal at the moment, but will be formalised with more research and prototyping. Gas of operations `SLOAD` and `SSTORE` increases by `X` gas when the storage slots accessed (read by `SLOAD` or written by `SSTORE`) were not previously accessed (by another `SLOAD` or `SSTORE`) during the same transaction. + +Future variant (will be possible after the implementation of the *Gross contract size acccounting*) is researched, where the increase is varied +depending on the size of the contract storage, i.e. `SLOAD` and `SSTORE` for smaller contracts will be cheaper. + +## Rationale + +[EIP-1884](https://eips.ethereum.org/EIPS/eip-1884) seeks to increase the gas cost of `SLOAD` but using a different justification +(latency of the execution as described in the Motivation). This EIP is likely to increase the cost of `SLOAD` by a larger amount, therefore partially +(because EIP-1884 also proposed other increases) supersedes EIP-1884. + +[EIP-2028](https://eips.ethereum.org/EIPS/eip-2028) describes the model that can be used for deciding the gas cost of data transmission. It is relevant +because in the stateless client regime `SSTORE` and `SLOAD` operations add more data to be transmitted (as well as computation to verify the proofs). + +The main alternate design is the rent proportional to the size of the contract storage, which unfortunately introduces a serious griefing +vulnerability problem, and so far the solution seems to be in redesigning and rewriting smart contracts in a way, which makes them not vulnerable. +However, this approach is likely to be very expensive on the non-technical (ecosystem) level. + +## Backwards Compatibility + +This change is not backwards compatible and requires hard fork to be activated. +There might also be an adverse effect of this change on the already deployed contract. It is expected that after this EIP and +[EIP-2026](https://eips.ethereum.org/EIPS/eip-2026) (rent prepayment for accounts), the recommendation will be made to raise the gas limit. This can somewhat dampen the +adverse effect of EIP. The most problematic cases would be with the contracts that assume certain gas costs of `SLOAD` +and `SSTORE` and hard-code them in their internal gas computations. For others, the cost of interacting with the contract +storage will rise and may make some dApps based on such interactions, non-viable. This is a trade off to avoid even bigger +adverse effect of the rent proportional to the contract storage size. However, more research is needed to more fully +analyse the potentially impacted contracts. + +## Test Cases + +Tests cases will be generated out of a reference implementation. + +## Implementation + +There will be proof of concept implementation to refine and clarify the specification. + +## Copyright +Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/). +