[Ethereum] How much does it cost to use a contract

contract-invocationgasgas-pricetransactions

Still new to ethereum and would like to know the price for a contract.

Best Answer

The total cost of a transaction that creates a contract or executes a contract is based on 2 factors:

gasUsed is the total gas that is consumed

gasPrice specified in the transaction

Total cost = gasUsed * gasPrice

gasUsed

Each operation in the Ethereum Virtual Machine (EVM) was assigned a number of how much gas it consumes. gasUsed is summing up all the gas for all the operations executed. There is a spreadsheet which offers a glimpse to some of the analysis behind them.

For estimating gasUsed, there is an estimateGas API with some caveats.

gasPrice

A user constructs and signs a transaction, and each user may specify whatever gasPrice they desire, this includes zero. However, the Ethereum clients launched at Frontier had a default gasPrice of 0.05e12 wei. As miners optimize for their revenue, if most transactions are being submitted with a gasPrice of 0.05e12 wei, it would be difficult to convince a miner to accept a transaction that specified a lower, or zero, gasPrice. How the default was chosen is asked in this question.

Example

Let's take a contract that just adds 2 numbers. From the spreadsheet above ADD consumes 3 gas.

The approximate cost, using the default gas price, would be:

3 * 0.05e12 = 1.5e11 wei

Since 1 Ether is 1e18 wei, the total cost would be 0.00000015 Ether.

This is a simplification since it ignores some costs, such as the cost of passing the 2 numbers to contract, before they can even be added.

Related Solutions

[Ethereum] When calling a smart contract function, who gets paid and how much does the caller pay

A specifies a gas price.

M1 and M2 decide whether to mine A's transaction if the gas price is high enough. If A's gas price was 1.5 GWei/gas, then only M1 would choose to mine A's transaction (since M2 wants 2 GWei/gas).

A always pays 1000 (given F costs 1,000 gas) multiplied by the gas price it specified; miners cannot change the transaction fee A pays and can only choose whether to include A's transaction in a block.

Only the winning miner gets the transaction fee paid by A. Other miners and all other (full) nodes do have to verify the transaction and store its results: yes, it's unfair to them and part of the problem related to incentives and scalability.

More information, https://blog.ethereum.org/2014/02/01/on-transaction-fees-and-the-fallacy-of-market-based-solutions

For each individual transaction that a miner includes, the costs are borne not just by that miner, but by every single node in the entire network.

[Ethereum] Simple example for gas cost

I agree with gatb27 about using Browser Solidity to get a feel for it.

Here's a little toy that does approximately what you described. Paste the code, click create, and then set a name.

setName() expects you to provide a quoted address and hex string like this (copy/paste should work):

"0x35ef07393b57464e93deb59175ff72e6499450cf","0x1"

You can get the set values back with the other function and just the address.

pragma solidity ^0.4.6;

contract PlayWithGas {

  mapping(address => bytes32) names;

  function setName(address userAddress, bytes32 name) returns(bool success) {
    names[userAddress] = name;
    return true;
  }

  function getName(address userAddress) returns(bytes32 name) {
    return names[userAddress];
  }
}