Gas Optimization Techniques for Storage

Since storage operations are costly in Solidity, optimizing how and when storage is used can save a significant amount of gas. Below are best practices developers should follow to build efficient smart contracts.

1. Use Memory or Calldata for Temporary Variables

Avoid unnecessary storage writes for temporary data.
Use memory or calldata for function parameters and local variables.

Example: Using memory instead of copying data to storage.


function process(uint256[] memory arr) public pure returns (uint256) {
    return arr.length;
}

2. Pack Variables

Solidity stores variables in 32-byte storage slots. Packing smaller variables together can significantly reduce storage usage.


struct Packed {
    uint8 a;
    uint8 b;
    uint16 c; // All fit in one 32-byte slot
}

This approach reduces the number of storage slots used and lowers gas costs.

3. Minimize Storage Writes

Reading and writing to storage multiple times is expensive. Instead, read once, operate in memory, and write back once.


function increment() public {
    uint256 temp = storedData; // Read once
    temp += 1;
    storedData = temp; // Write once
}

4. Use Immutable and Constants

Variables marked as constant or immutable do not occupy storage slots, making them much cheaper.


uint256 public constant MAX = 100; // No storage cost

5. Delete Unused Storage

Using the delete keyword clears storage slots and refunds some gas.


delete storedData;

Summary Table

Feature	Storage	Memory	Calldata
Persistence	Permanent	Temporary	Temporary
Modifiable	Yes	Yes	No
Cost	High	Medium	Low
Use Case	State variables	Local variables	External parameters