Removes Accounts Delta Hash

Summary

With the introduction of the Accounts Lattice Hash (SIMD-215), the merkle-based Accounts Delta Hash is redundant and can be removed.

Motivation

This SIMD follows on from SIMD-215, and shares its motivation:

The main goal is to scale Solana to billions accounts

When a block is done being processed, it is frozen. The bank hash is calculated during the freezing process, and includes calculating the Accounts Delta Hash. The Accounts Delta Hash is the merkle-based hash of the accounts modified in this block. As established in SIMD-215, merkle-based hashing of accounts hinders scaling. And since SIMD-215 added the Accounts Lattice Hash, which is a hash of the total account state, the merkle-based hash of only the accounts modified per block is redundant. Therefore the Accounts Delta Hash can be removed from the bank hash entirely.

New Terminology

None.

Detailed Design

Remove the Accounts Delta Hash from the Bank Hash.

Alternatives Considered

None.

Impact

Only validators will be impacted, and their performance will improve since the merkle-based hashing of modified accounts per block will no longer be performed.

Security Considerations

None.

Backwards Compatibility

Incompatible. This changes the bank hash, thus changing consensus.