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Update EIP-7691: add update fraction specification #9060

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Dec 5, 2024
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Update EIP-7691: add update fraction specification #9060

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EIP-7691: add update fraction specification
adietrichs Nov 28, 2024
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EIP-7691: add update fraction rationale
adietrichs Nov 28, 2024
8506d68
EIP-7691: clarify fork timestamp
adietrichs Dec 5, 2024
25fa686
EIP-7691: rationale formatting fix
adietrichs Dec 5, 2024
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29 changes: 23 additions & 6 deletions EIPS/eip-7691.md
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Expand Up @@ -29,13 +29,16 @@ The current long term plan of Ethereum is to implement peerDAS as specified by [

### Parameters

| Constant | Value |
|----------------------------------|---------------------|
| `PECTRA_FORK_EPOCH` | `tbd` <!-- TODO --> |
| `MAX_BLOBS_PER_BLOCK_ELECTRA` | `9` |
| `TARGET_BLOBS_PER_BLOCK_ELECTRA` | `6` |
| Constant | Value |
|------------------------------------------|---------------------|
| `PECTRA_FORK_EPOCH` | `tbd` <!-- TODO --> |
| `MAX_BLOBS_PER_BLOCK_ELECTRA` | `9` |
| `TARGET_BLOBS_PER_BLOCK_ELECTRA` | `6` |
| `BLOB_BASE_FEE_UPDATE_FRACTION_ELECTRA` | `5007716` |

The values defined are consumed by the consensus layer clients and are passed via the engineAPI to the execution layer clients. The mechanism describing this uncoupling is specified in [EIP-7742](./eip-7742.md).
`MAX_BLOBS_PER_BLOCK_ELECTRA` and `TARGET_BLOBS_PER_BLOCK_ELECTRA` are consumed by the consensus layer clients, and starting at `PECTRA_FORK_EPOCH` replace the respective old max and target values. `TARGET_BLOBS_PER_BLOCK_ELECTRA` is then passed via the engineAPI to the execution layer clients. The mechanism describing this uncoupling is specified in [EIP-7742](./eip-7742.md).

`BLOB_BASE_FEE_UPDATE_FRACTION_ELECTRA` is consumed by the execution layer clients, and starting at `PECTRA_FORK_EPOCH` timestamp replaces the old update fraction value.

## Rationale

Expand All @@ -51,6 +54,20 @@ While this EIP may not achieve the new optimal blob limit, it offers a compromis

Through the use of big block/blob tests on Ethereum mainnet as well as testnets, we can earn a high degree of certainity that the blob limit increase would not negatively impact the network. These tests as well as the associated analysis can be performed mostly by non-client team entities, with minimal input required. Since the changes are quite contained, the EIP should be able to reduce the risk of the blob limit increase.

### Update Fraction

The original target and max values from [EIP-4844](./eip-4844.md) were at a 1:2 ratio. As a consequence, responsiveness to full and empty blob sections was symmetrical:

* full blobs: basefee increases by ~12.5%
* no blobs: basefee decreases by ~11.1%

The new target and max values from this EIP are at a 2:3 ratio, which breaks that symmetry.As a consequence, the basefee becomes significantly more responsive to empty blob sections (that are 6 blobs under target) than to full ones (that are 3 blobs over target). This is by design, as it takes two blocks with full blobs in a row to make up for a single block with no blobs. However, it creates the challenge of finding a good compromise base fee sensitivity level.
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Add space between "symmetry" and "As a consequence"


The `BLOB_BASE_FEE_UPDATE_FRACTION_ELECTRA` value in this EIP is chosen as the mid-point between keeping the responsiveness to full blobs and no blobs constant:

* full blobs: basefee increases by ~8.2%
* no blobs: basefee decreases by ~14.5%

## Backwards Compatibility

The consensus clients would continue to use `MAX_BLOBS_PER_BLOCK` for the deneb fork and once the `ELECTRA` fork is active, they would use `MAX_BLOBS_PER_BLOCK_ELECTRA`.
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