Gas optimization for L2 in Blockchain / Solidity

Introduction

Gas optimization helps save money and speed up transactions on Layer 2 blockchains. It makes using blockchain cheaper and faster.

When you want to reduce transaction fees on Layer 2 networks.

When building smart contracts that need to run efficiently on L2.

When sending many transactions and want to save overall gas costs.

When designing dApps that users expect to be fast and low-cost.

When optimizing contract code to avoid unnecessary operations.

Syntax

Blockchain / Solidity

// Example: Solidity function optimized for gas on L2
function add(uint a, uint b) external pure returns (uint) {
    unchecked {
        return a + b;
    }
}

Use unchecked to skip overflow checks when safe, saving gas.

Minimize storage writes and external calls to reduce gas costs.

Examples

This skips overflow checks, which saves gas if you know overflow won't happen.

Blockchain / Solidity

// Using unchecked to save gas
function increment(uint x) external pure returns (uint) {
    unchecked {
        return x + 1;
    }
}

Using smaller data types packs variables into one storage slot, reducing gas.

Blockchain / Solidity

// Packing variables to save storage
contract Example {
    uint128 a;
    uint128 b;
}

Only update storage if the value changes to save gas.

Blockchain / Solidity

// Avoiding unnecessary state changes
function setValue(uint newValue) external {
    if (value != newValue) {
        value = newValue;
    }
}

Sample Program

This contract shows two ways to save gas on L2: using unchecked for addition and avoiding storage writes when not needed.

Blockchain / Solidity

pragma solidity ^0.8.20;

contract GasOptimized {
    uint128 public count;

    // Increment count safely with gas optimization
    function increment() external {
        unchecked {
            count += 1;
        }
    }

    // Set count only if different to save gas
    function setCount(uint128 newCount) external {
        if (count != newCount) {
            count = newCount;
        }
    }
}

Important Notes

Gas costs on L2 are lower but still matter for user experience and cost.

Always test your contract on testnets to measure gas savings.

Use tools like Hardhat or Tenderly to analyze gas usage.

Summary

Gas optimization reduces transaction fees and speeds up L2 blockchain use.

Techniques include using unchecked math, packing variables, and minimizing storage writes.

Testing and measuring gas helps find the best optimizations.

Practice

1. Which of the following is a common method to reduce gas costs on Layer 2 blockchains?

easy

A. Using loops with many iterations

B. Increasing the block size limit

C. Adding more storage variables to the contract

D. Using calldata instead of memory for function inputs

Solution

1. Step 1: Understand calldata vs memory

   Calldata is cheaper than memory because it is read-only and does not require copying data.

2. Step 2: Identify gas saving method

   Using calldata for function inputs reduces gas compared to memory or storage.

3. Final Answer:

   Using calldata instead of memory for function inputs -> Option D

4. Quick Check:

   Calldata is cheaper than memory [OK]

Hint: Choose calldata for inputs to save gas on L2 [OK]

Common Mistakes:

• Thinking increasing block size reduces gas
• Assuming more storage variables save gas
• Using loops without optimization

2. Which Solidity syntax correctly declares a function parameter to use calldata for gas optimization on L2?

easy

A. function foo(string memory data) external {}

B. function foo(string calldata data) external {}

C. function foo(string storage data) external {}

D. function foo(string data) external {}

Solution

1. Step 1: Recall parameter data location keywords

   Solidity allows memory, storage, or calldata for reference types in parameters.

2. Step 2: Identify calldata usage

   Calldata is specified explicitly as string calldata for external functions to save gas.

3. Final Answer:

   function foo(string calldata data) external {} -> Option B

4. Quick Check:

   Calldata keyword used correctly [OK]

Hint: Use 'calldata' keyword for external function parameters [OK]

Common Mistakes:

• Using memory instead of calldata for external inputs
• Omitting data location keyword
• Using storage incorrectly in parameters

3. What will be the gas cost difference when using unchecked math in Solidity on L2 compared to normal math?

medium

A. Gas cost decreases because overflow checks are skipped

B. Gas cost increases due to extra checks

C. Gas cost stays the same

D. Gas cost is unpredictable

Solution

1. Step 1: Understand unchecked math

   Unchecked math skips overflow and underflow checks, saving gas.

2. Step 2: Compare gas costs

   Skipping checks reduces gas cost compared to normal safe math operations.

3. Final Answer:

   Gas cost decreases because overflow checks are skipped -> Option A

4. Quick Check:

   Unchecked math saves gas by skipping checks [OK]

Hint: Unchecked math skips checks, lowering gas [OK]

Common Mistakes:

• Assuming unchecked math adds overhead
• Believing gas cost is unchanged
• Ignoring overflow risks

4. Given this Solidity snippet on L2, what is the main issue causing higher gas usage?

uint256 public count;
function increment() external {
  count = count + 1;
}

medium

A. Missing unchecked block for increment

B. Using public variable instead of private

C. Function should be view instead of external

D. No issue, code is optimal

Solution

1. Step 1: Identify gas cost in arithmetic

   Normal addition includes overflow checks increasing gas.

2. Step 2: Suggest unchecked usage

   Wrapping increment in unchecked { count += 1; } saves gas by skipping checks.

3. Final Answer:

   Missing unchecked block for increment -> Option A

4. Quick Check:

   Unchecked block reduces gas for safe increments [OK]

Hint: Use unchecked for simple increments to save gas [OK]

Common Mistakes:

• Thinking public visibility affects gas here
• Confusing external with view function
• Assuming code is already optimized

5. You want to optimize a Layer 2 contract that stores multiple small variables. Which approach best reduces gas usage?

hard

A. Use dynamic arrays for all variables

B. Store each variable in separate storage slots for clarity

C. Pack multiple uint8 variables into a single uint256 storage slot

D. Avoid using calldata and always copy to memory

Solution

1. Step 1: Understand storage slot packing

   Multiple small variables like uint8 can fit into one 256-bit slot, saving gas.

2. Step 2: Compare storage strategies

   Separating variables wastes slots; dynamic arrays add overhead; calldata usage unrelated here.

3. Final Answer:

   Pack multiple uint8 variables into a single uint256 storage slot -> Option C

4. Quick Check:

   Storage packing reduces gas by slot sharing [OK]

Hint: Pack small vars into one slot to save gas [OK]

Common Mistakes:

• Using separate slots wastes gas
• Overusing dynamic arrays increases cost
• Ignoring calldata benefits in storage