Gas optimization for L2 in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is 'gas' in the context of Layer 2 (L2) blockchain solutions?

Gas is the fee required to perform transactions or execute smart contracts on a blockchain. In L2, gas costs are usually lower than on Layer 1 because transactions are processed off-chain or in batches.

beginner

Why is gas optimization important for Layer 2 solutions?

Gas optimization reduces transaction costs and improves user experience by making operations cheaper and faster, which encourages more usage of L2 networks.

intermediate

Name one common technique to optimize gas usage on L2.

Batching multiple transactions together to reduce the total gas cost per transaction is a common gas optimization technique on L2.

intermediate

How does data compression help in gas optimization on L2?

Data compression reduces the size of transaction data that needs to be posted on-chain, lowering the gas fees because less data consumes less gas.

intermediate

What role do calldata and calldata gas costs play in L2 gas optimization?

Calldata is the data sent with a transaction. Optimizing calldata size and usage reduces gas costs because calldata gas is charged based on data size.

What is a primary benefit of using Layer 2 solutions for gas optimization?

A Lower transaction fees compared to Layer 1

B Increased block size on Layer 1

C More complex smart contracts

D Slower transaction confirmation

Layer 2 solutions reduce transaction fees by processing transactions off-chain or in batches, lowering gas costs.

Which technique helps reduce gas fees by combining multiple transactions into one?

A Data encryption

B Batching

C Token staking

D Proof of Work

Batching groups multiple transactions to share gas costs, reducing the fee per transaction.

Why is minimizing calldata size important for gas optimization on L2?

A Because calldata stores smart contract code

B Because calldata is free

C Because calldata increases block time

D Because calldata gas cost depends on data size

Calldata gas cost is proportional to the amount of data sent, so smaller calldata means lower gas fees.

Which of the following is NOT a gas optimization strategy on L2?

A Data compression

B Batching transactions

C Increasing gas price

D Optimizing calldata usage

Increasing gas price raises costs and is not an optimization strategy.

How does Layer 2 improve transaction speed alongside gas optimization?

A By processing transactions off-chain or in batches

B By increasing Layer 1 block size

C By requiring more confirmations

D By using slower consensus algorithms

L2 processes transactions off-chain or in batches, speeding up confirmation and reducing gas fees.

Explain how batching transactions helps reduce gas costs on Layer 2.

Think about how sharing costs works in real life, like carpooling.

Describe why optimizing calldata size is important for gas optimization on L2.

Imagine sending a letter: smaller letters cost less to send.

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