rollup_plasma_gas_estimations.py

# Batch exit strategy (known as a checkpoint in our model):
# 1) input is a bytes string of all exits
# 2) merklize all of the exits
# 3) store the root hash as a batch exit

exit_bytes = 64  # Each exit we store 14 bytes for start, 14 bytes for end, and 4 bytes for block number
cd_gas_per_byte = 68
gas_per_sstore = 20000
gas_cost_of_merkle_root = gas_per_sstore
cd_gas_per_exit = cd_gas_per_byte * exit_bytes
total_gas_in_block = 8000000
def sha3_gas(num_bytes):
    num_words = num_bytes // 32
    return 30 + 6 * num_words

sha3_gas_of_one_hash = sha3_gas(32)
gas_for_one_set_of_exits = sha3_gas(exit_bytes) + cd_gas_per_exit + sha3_gas_of_one_hash
# Note: Added `sha3_gas_of_one_hash` gas cost per exit because merkle tree hash cost is 2x number of leaves
total_exits_in_block = ((total_gas_in_block - gas_cost_of_merkle_root) / gas_for_one_set_of_exits)
print('total exits in block:', total_exits_in_block)
print('gas per exit:', total_gas_in_block / total_exits_in_block)
eth_block_time = 14
print('avg exits per second', total_exits_in_block//eth_block_time)

# Results:
# total exits in block: 1801.354401805869
# gas per exit: 4441.102756892231
# avg exits per second 128.0

# Note: For optimistic rollup, assuming all eth blocks are filled, the `*max* safe tps = (dispute_period/halt_time) * tps`