How to estimate gas usage?

Question

Please stop me if I am wrong.

When we call any "state-changing" function of smart contract, this function will be run by all the miners of the mainnet. As a caller, I need to pay this using the ether and whenever I use the metamask, it estimates how much it will cost.

Here is what I am not sure

How to even estimate the number of miners? we don't know how many miners are there or how many of them will run my function? If I paid X amount and there are more miners than I paid, it won't be runnable by other miners.

How is this handled? Am I missing something?

Answer 1

The gas fee for executing a state-changing function in a smart contract is the sum of:

1. The total cost of the executed opcodes, where each opcode has a specific cost
2. The total cost of changed storage slots (states), where:
   • Changing a slot from zero to non-zero costs 20000 gas
   • Changing a slot from non-zero to non-zero costs 10000 gas
   • Changing a slot from non-zero to zero refunds 5000 gas (under certain restrictions)

The whole thing depends on the actual state of the blockchain at the time of execution.

For example, the cost of executing:

if (someContract.someNonPureFunction()) {
    // do something
}
else {
    // do something else
}

Depends on the state of someContract.

That's why the whole thing is referred to as gas-estimate.

As you understand, the number of miners on the network has nothing to do with all of this.

As far as you're concerned, you may assume that there's a single miner that you are paying to.