Octane no empty blocks

[ttarsi]

Problem to Solve

In the early days of the chain, many EVM blocks are empty. This wastes space on nodes in the long run. We could reduce node size significantly by skipping "most" empty blocks.

Proposed Solution

First thing to decide is whether periodic empty blocks are required or not, i.e. at least build one empty block every N consensus blocks.

Then, there are basically two ways to do this:

1. Best effort per node config

• Provide an halo config flag (evm-no-empty-blocks).
• If enabled on a validator node, that node proposes skips execution payload if it contains zero txs, or if ConsensusHeight%N==0
• No other changes are required, since validators are allowed to skip EVM blocks when proposing consensus blocks.
• This will however depend on the proportion of validators that configure this.

2. Enforced in consensus layer

• Don't provide any flag, rather build this as network upgrade.
• All validators skips execution payload it contains zero txs, or if ConsensusHeight%N==0
• All validators enforce this in ProcessProposal. So reject empty evm blocks unless ConsensusHeight%N==0.