Gas adjustment of the smart contract function

Question

I have function which uses for loops on the calldata array as following:

mapping (address => bool) public userRegistered;
function registerUsers(address[] calldata users) external {
  for (uint256 i; i < users.length; ++i) {
    userRegistered[users_[i]] = true;
  }
}

Context of the function doesn't matter, I just shortened the actual function to give the idea. So I know the block gas limit on ethereum is 15M, but maximum it can be 30M. I want to put a constraint on the length of the users_ array so it does not hit block gas limit ever causing so much loss of money.

I am planning to pick such a maximum length that, gas cost will be very close to the block gas limit. But my confusion is, should I arrange according to 15M or 30M limit? For instance when the network is rather empty at that point and the produced blocks are mostly consist of 15M gas limit, and I submit the tx that will require 29.9M gas, will it not be executed or will the execution will be much slower?

Answer 1

You can definitely submit the transaction with 29.9M gas at any point and rest assured that it can be included in a block, regardless of current congestion. You do need to be aware that buying out a block like that basically means you need to pay a higher miner tip gas price than any other transaction in the mempool, so you'll likely end up paying more on average for a full block transaction than if you went for a lower limit