Increase MIN_BASE_FEE_PER_BLOB_GAS

Abstract

This EIP proposes an increase to the MIN_BASE_FEE_PER_BLOB_GAS to speed up price discovery on blob space. It also resets the excess blob gas to 0, to avoid a blob base fee spike.

Motivation

When scoping 4844, the thinking was that blobs would only enter price discovery once, relatively quickly after the blob rollout; however, this has not been the case. In fact, blobs have entered price discovery several times, and the frequency of price discovery events is likely to increase in the short term as we approach saturation of capacity. Moreover, the roadmap calls for further increases in blob capacity in subsequent hardforks, which may lead to price discovery events happening around those changes in the future.

Increasing the MIN_BASE_FEE_PER_BLOB_GAS will speed up price discovery on blob space.

Specification

MIN_BASE_FEE_PER_BLOB_GAS Increase

The main specification change introduced by this EIP is setting MIN_BASE_FEE_PER_BLOB_GAS to 2**25:

+ MIN_BASE_FEE_PER_BLOB_GAS  =  2**25
- MIN_BASE_FEE_PER_BLOB_GAS = 1

excess_blob_gas Reset

To avoid a blob base fee spike, the calc_excess_blob_gas is modified to reset excess_blob_gas to 0 at the fork. To detect the fork height, the block timestamp needs to be passed into calc_excess_blob_gas.

def calc_excess_blob_gas(parent: Header, block_timestamp: int) -> int:
    # at the fork, set excess_blob_gas to 0
    if parent.timestamp < FORK_TIMESTAMP and block_timestamp >= FORK_TIMESTAMP:
        return 0
    
    # otherwise, calculate normally
    ...

validate_block needs to be updated to pass the block timestamp into calc_excess_blob_gas:

def validate_block(block: Block) -> None:
    ...

    # add timestamp parameter
    assert block.header.excess_blob_gas == calc_excess_blob_gas(block.parent.header, block.header.timestamp)

    ...

Rationale

The current MIN_BASE_FEE_PER_BLOB_GAS is 1 wei. This is many orders of magnitude lower than the prevailing price of blobs when blobs enter price discovery. Whenever demand for blobs exceeds supply, blobs enter price discovery, but traversing the 8 orders of magnitude between 1 wei and the point where elasticity of demand starts to decrease takes a long time.

The blob base fee can at most double every $\log_{1.125}(10) = 5.885$ blocks when blocks use all available blob space. When blobs enter price discovery, they must climb many factors of 2 to reach the prevailing price.

To set the parameter appropriately, one approach is to look at the cost of simple transfers when base fees are low. The cost of a simple transfer when the base fee is 1 GWEI is ~5 cents USD at today's prices (2,445.77$ ETH/USDC). We can try to peg the minimum price of a blob to that. Today, to reach this price, it requires an excess blob gas of 63070646. When you calculate how long this would take to reach from 0 excess blob gas, you get:

63070646/(3 * 2**17) = 160.396947225

The closest power of 2 to the corresponding reserve price would be MIN_BASE_FEE_PER_BLOB_GAS = 2**27. Out of an abundance of caution, we will go with MIN_BASE_FEE_PER_BLOB_GAS = 2**25 to ensure that even if the price of ETH rises significantly, the reserve price will not be set too high. This value corresponds to a minimum blob price of ~1 cent at today's prices (2,445.77$ ETH/USDC). Further, decreasing the MIN_BASE_FEE_PER_BLOB_GAS beyond 2**25 would slow down price discovery without a significant decrease in the price of blobs when the network is unsaturated.

Below you will find a plot provided by @dataalways showing the fraction of type 3 transaction fees that are paid in blob base fees for different values of MIN_BASE_FEE_PER_BLOB_GAS. Note that even after the proposed change, for historical values of l1 gas, the price of blobs would have been dominated by the price of the L1 gas.

Backwards Compatibility

This EIP is not backwards compatible and requires a coordinated upgrade across all clients at a specific block number.

Security Considerations

Rollups that use blobs as a data availability layer will need to update their posting strategies.

Copyright

Copyright and related rights waived via CC0.