[Ethereum] How to decide the amount of ether you need for your app

ethergas

Let say I am building a contract which works like a coins/mark point system. I know that when we deploy the contract we need ether. And the transaction will happen which then needs gas for the fee. The gas will be extracted from the ether that the account has right?

The gas is said to be consistent but the number of transaction cannot be predicted. It can be few or huge so how we calculate the ether we need in first place? (I am asking this in case you build an app then release to customer, how you should set up the ether amount and make sure later it not runs out)

Anyone with experience in DApp development out there please help explains how should we allocate ether in first place? And what to do when the ether runs out?

Many thanks

Best Answer

It sounds like you have a few fundamental things you're getting confused about with contracts and ether: Firstly, you as a human (or company) owns an Ethereum address which you can use to transfer ether into and out of (your wallet). When you deploy a contract, that action is a transaction in the Ethereum blockchain, and so has to come from some Ethereum address. So, you sign it with your wallet address, and the Ethereum virtual machine creates a brand new address (separate from your own wallet address) for the new contract.

Anyone can send ether to a contract. But getting ether back out is dependent on the code of the contract itself. You need to pick how that's going to work as you develop it.

So, to answer your questions:

The gas [to deploy the contract] will be extracted from the ether that the account has right?

The account that's deploying the contract (your wallet) must have enough ether in it to pay for the gas to create the contract, yes. The newly-created contract will be created with no ether in it (unless the code of the contract does something that transfers ether in).

The gas is said to be consistent but the number of transaction cannot be predicted. It can be few or huge so how we calculate the ether we need in first place?

The amount of gas needed to create a new Contract depends on the code complexity of the Contract itself. You can use the estimateGas() function in web3 to calculate that from the compiled bytecode of your contract before you deploy it (more details).

How you should set up the ether amount and make sure later it not runs out

Both your own personal wallet and any deployed contract can receive ether paid to it. So, if your deployed contract needs to send ether to someone, and it runs out, you can send more to it at a later time. However, it's possible that a contract, once deployed, will not ever need any ether, since it doesn't pay for the gas needed to trigger its methods. A transaction needs to be crafted to call functions on that contract, and that calling function has to come from a human-owned contract, and the human-owned contract pays for the gas of the transaction.

Related Solutions

[Ethereum] Disable mining/gas/ether or set really low

There are several different options for a private/consortium chain setup:

Use a custom genesis block to set the difficulty level for mining to make it less intensive. Only turn mining on for some of the nodes that are participating in the network. In addition, you can pre-fund specific accounts
Use something like Parity's Proof of Authority chain to configure who the validators for the chain will be
Create a permissioned ledger using something like HydraChain that does not require Proof of Work and provides faster block generation in addition to full customization of gas, transaction fees, etc...

These approaches should address some of your questions. But keep in mind gas plays an important role when it comes to the execution of contracts. One of the main motivations behind gas is to prevent the Halting problem. Which means without gas, it would be possible to create a contract that could potentially run forever opening up the possibility of various attacks such as Denial Of Service.

[Ethereum] how to estimate gas cost

Using Truffle and testrpc. It's actually pretty easy to build a development environment and test different use cases.

For the gas estimation, it's mostly based on Web3 native functions:

You can retrieve the gas price (in wei) using web3.eth.getGasPrice
The function estimateGas will give the gas estimation for a function (with the parameters passed)
Multiply number of gas by gas price to get the gas cost estimation.

For example

var TestContract = artifacts.require("./Test.sol");

// Run unit tests to populate my contract
// ...
// ...

// getGasPrice returns the gas price on the current network
TestContract.web3.eth.getGasPrice(function(error, result){ 
    var gasPrice = Number(result);
    console.log("Gas Price is " + gasPrice + " wei"); // "10000000000000"

    // Get Contract instance
    TestContract.deployed().then(function(instance) {

        // Use the keyword 'estimateGas' after the function name to get the gas estimation for this particular function 
        return instance.giveAwayDividend.estimateGas(1);

    }).then(function(result) {
        var gas = Number(result);

        console.log("gas estimation = " + gas + " units");
        console.log("gas cost estimation = " + (gas * gasPrice) + " wei");
        console.log("gas cost estimation = " + TestContract.web3.fromWei((gas * gasPrice), 'ether') + " ether");
    });
});

Result in my case (private network):

> truffle test
Using network 'test'.

Compiling .\contracts\Migrations.sol...
Compiling .\contracts\Test.sol...

Gas Price is 20000000000 wei
gas estimation = 26794 units
gas cost estimation = 535880000000000 wei
gas cost estimation = 0.00053588 ether

Best Answer

Related Solutions

[Ethereum] Disable mining/gas/ether or set really low

[Ethereum] how to estimate gas cost

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