Introduce a new Verkle state tree alongside the existing hexary Patricia tree. After the hard fork, the Verkle tree stores all edits to state and a copy of all accessed state, and the hexary Patricia tree can no longer be modified. This is a first step in a multi-phase transition to Ethereum exclusively relying on Verkle trees to store execution state.
Motivation
Verkle trees solve the key problem standing in the way of Ethereum being stateless-client-friendly: witness sizes. A witness accessing an account in today’s hexary Patricia tree is, in the average case, close to 3 kB, and in the worst case it may be three times larger. Assuming a worst case of 6000 accesses per block (15m gas / 2500 gas per access), this corresponds to a witness size of ~18 MB, which is too large to safely broadcast through a p2p network within a 12-second slot. Verkle trees reduce witness sizes to ~200 bytes per account in the average case, allowing stateless client witnesses to be acceptably small.
The Ethereum state will likely replace Merkle Trees by Verkle Trees for storage in the future.
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