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 There is emprical analysis (unpublished, but will be) suggesting that 1 uncached `SSTORE` or `SLOAD` adds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
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.
