EIP-7642 - eth/69 - history expiry and simpler receipts

Abstract

This EIP modifies the 'eth' p2p protocol to announce the historical block range served by the node. We also simplify the handshake to remove total difficulty information, which isn't used anymore after the merge. Additionally we propose to remove the Bloom field from receipts transfered over the protocol.

Motivation

Block range in Status message

In the history expiry working group, it was decided that clients may drop pre-merge history from their storage after May 1, 2025. For clients that want to sync history through the 'eth' protocol, it is essential to know whether a peer still serves old history. A similar idea was proposed in EIP-7542 but was later withdrawn because a political decision on history expiry had not been reached at the time.

Removing Bloom in Receipts

We recently discovered that none of the clients store the Bloom field of the receipts as it can be recomputed on demand. However the networking spec requires the Bloom field to be sent over the network. Thus a syncing node will ask for the Bloom filters for all receipts. The serving node will regenerate roughly 530GB of bloom filters (2.3B txs * 256 byte). These 530GBs are send over the network to the syncing peer, the syncing peer will verify them and not store them either. This adds an additional 530GB of unnecessary bandwidth to every sync.

BlockRangeUpdate message

We want clients to be aware of the available block range in their peers. The new notification message can be used to detect sync status of peers, and adjust fetching behavior accordingly.

Specification

Status message changes

Modify the Status (0x00) message as follows:

• (eth/68): [version: P, networkid: P, td: P, blockhash: B_32, genesis: B_32, forkid]

• (eth/69): [version: P, networkid: P, genesis: B_32, forkid, earliestBlock: P, latestBlock: P, latestBlockHash: B_32]

Note blockhash has moved to the end to match BlockRangeUpdate.

Receipts message changes

Modify the encoding for receipts in the Receipts (0x10) message as follows:

• (eth/68): receipt = {legacy-receipt, typed-receipt} with

typed-receipt = tx-type || rlp(legacy-receipt)

legacy-receipt = [
    post-state-or-status: {B_32, {0, 1}},
    cumulative-gas: P,
    bloom: B_256,
    logs: [log₁, log₂, ...]
]

• (eth/69): receipt = [tx-type, post-state-or-status, cumulative-gas, logs]

BlockRangeUpdate message

Add a new BlockRangeUpdate (0x11) message, with the following encoding

[earliestBlock: P, latestBlock: P, latestBlockHash: B_32]

The new message should be sent whenever the block range available from this client is updated. In order to reduce traffic, it is not necessary to send an update for every new block. Clients should send an update at most once per epoch (32 blocks).

Rationale

Status changes

After the merge, the TD field of the Status message became meaningless since the difficulty of post-merge blocks are 0. It could in theory be used to distinguish synced with unsynced nodes, but the same thing can be accomplished with the forkid as well.

The new earliestBlock field is technically not required for history expiry, but there are a couple reasons why adding it can help:

• It improves peer finding for clients that still want to sync history from p2p after the agreed-upon removal of pre merge history has taken place. Without earliestBlock, the client would have to perform a request for history to check if the earlier range exists, and assume that a failed request means it's not there.
• The new field can be used for census in a specialized crawler. We will be able to see how many users/nodes enable history, and in which implementation.
• It prepares us for a future where the history expiry window is dynamic.

Receipts changes

Removing the bloom filters from the Receipt message reduces the CPU load of serving nodes as well as the bandwidth significantly. The receiving nodes will need to recompute the bloom filter in order to fully verify the receipt hash. The recomputation is not very CPU intensive. The bandwidth gains amount to roughly 530GiB per syncing node or (at least) 95GiB snappy compressed.

In Ethereum consensus, the encoding of receipts differs between legacy transactions and typed transactions. Typed transaction receipts are 'opaque' and have the data wrapped in a byte array. However, all receipt types ultimately contain the same four fields. With the removal of the bloom filter, the networking protocol now deviates from the encoding used by consensus, and there is no need to replicate the weird and expensive encoding used there. The proposed receipt encoding is just a flat list of the required data fields.

Backwards Compatibility

This EIP changes the eth protocol and requires rolling out a new version, eth/69. Supporting multiple versions of a wire protocol is possible. Rolling out a new version does not break older clients immediately, since they can keep using protocol version eth/68.

This EIP does not change consensus rules of the EVM and does not require a hard fork.

Security Considerations

None

Copyright

Copyright and related rights waived via CC0.