How to reduce Ethereum GasCost when executing multiple sequence of actions within 1 transaction?

Question

I am trying to execute multiple sequence of actions within a single transaction. But, I think I am ending up using heavy GasCost and I am trying to find a solution to optimise the code to reduce Gas Fees. Here is my setup.

I am encoding all the required actions into arrays using Web3's web3.eth.abi.encodeFunctionCall and sending them to my smart contract code which executes each of the actions in a for loop.

JS file.

let abi1 = web3.eth.abi.encodeFunctionCall( { "name": "deposit", "type": "function", "inputs": [ { "name": "_amount", "type": "uint256" } ] }, [web3.utils.toWei((1000).toString(), 'Ether')] );

let abi2 = web3.eth.abi.encodeFunctionCall( {"constant":false,"inputs":[],"name":"withdrawAll","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"}, [] );

The above is stored in Arrays in JS file.

addrs = [address1, address2];
actions = [abi1, abi2];

I am passing these arrays to my smart contract which receives them like -

function execute(address[] calldata _addrs, bytes[] calldata _actions)
{
     for(uint i = 0; i < _addrs.length; i++)
        address(_addrs[i]).call(_actions[i]);
}

I try to get the Gas estimate using the following code:

const [gasPrice, gasCost] = await Promise.all([
   web3.eth.getGasPrice(),
   tx.estimateGas({from: address}),
]);

console.log("gasPrice = ", gasPrice);
console.log("gasCost = ", gasCost);

I get the estimate as - gasPrice: 66 Gwei and gasCost: 1443172. But, when I execute the transaction, with 70 Gwei, the actual GasCost used is 3,314,500. I think this is way too high, cause, I have seen similar transactions which uses way less GasCost, but, higher Gwei. Does that mean, I have to use high Gwei to reduce total Gas fee Spent?

I would like to know the best coding methods that I can implement to optimise the execution of the smart contract and in turn reduce gas fees used. I am sure there are many other methods to execute these sequence of actions within 1 transaction. Can someone point me in the right direction in order to achieve this?

Answer 1

I should see your complete smart contract to see the logic of your DApp. But here are some general tips that you can do in your contract to reduce the gas cost:

• Use fixed array sized if you can(use bytes1 to bytes32).
• Do not use loops in your functions(use single action in a function) unless necessary.
• Avoid modifying storage variables in a loop, it can be so expensive. You can see this link for more information on saving gas: https://medium.com/coinmonks/optimizing-your-solidity-contracts-gas-usage-9d65334db6c7