Medição de gas
Ferramentas de criação de perfis
Medição de gas é uma aula grátis de Web3 & DApp Development Fundamentals no CoddyKit. Esta é a aula 4 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Web3 & DApp Development Fundamentals, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Web3 & DApp Development Fundamentals inclui 4 aulas no total.
Partes desta aula ainda não foram traduzidas e aparecem em inglês.
Measure, Don't Guess
Gas optimization without measurement is guesswork. The compiler, opcode costs, and access patterns interact in non-obvious ways, so an intuitive change can sometimes make things worse.
Always profile before and after. A change that does not reduce measured gas is not an optimization, no matter how clever it looks.
Forge Gas Reports
Foundry's forge test --gas-report prints a per-function table of min, average, median, and max gas usage across all your tests. It is the fastest way to spot expensive functions.
$ forge test --gas-report
| Function | min | avg | median | max | # calls |
| transfer | 28012 | 34521 | 34521 | 51012 | 12 |
| approve | 24300 | 24300 | 24300 | 24300 | 5 |Gas Snapshots
forge snapshot writes the gas cost of every test to a .gas-snapshot file. Commit it to version control, then run forge snapshot --diff to see exactly how a change affected gas.
This turns gas regressions into reviewable diffs in pull requests.
$ forge snapshot
$ forge snapshot --diff
testTransfer() (gas: -1240 (-3.6%))
testMint() (gas: +85 (+0.2%))Measuring in Tests
For fine-grained measurement, read gasleft() before and after a call inside a test. The difference is the gas consumed by that block of code.
uint256 before = gasleft();
target.doWork();
uint256 used = before - gasleft();
emit log_named_uint("gas used", used);Verbose Traces
Running tests with -vvvv shows a full execution trace including the gas cost of each external call and opcode group. This reveals where gas is spent, not just the total.
$ forge test --match-test testTransfer -vvvv
[34521] Token::transfer(bob, 100)
emit Transfer(from: alice, to: bob, value: 100)
return: trueThe Optimizer Setting
The Solidity optimizer changes runtime and deployment gas. The runs parameter is a hint about how often functions are called.
- Low
runs(e.g. 1) optimizes for cheap deployment - High
runs(e.g. 10000) optimizes for cheap repeated calls
Set it in foundry.toml and always measure with the optimizer enabled, since it reflects production behavior.
# foundry.toml
[profile.default]
optimizer = true
optimizer_runs = 10000Comparing Implementations
To compare two approaches, write a test that exercises each under identical conditions and inspect the gas report side by side.
Keep inputs the same and isolate the change to one variable, otherwise you cannot attribute the gas difference to the optimization you made.
function testNaive() public { c.sumNaive(data); }
function testOptimized() public { c.sumOptimized(data); }
// compare both rows in --gas-reportBeware Warm vs Cold Skew
Gas reports can mislead because the first access in a test is cold and later ones are warm. A function called once in setup may show a higher cold cost than the same function later.
Look at min, median, and max columns together rather than a single average, and design tests that reflect real-world access patterns.
Etherscan and Real Receipts
On-chain transaction receipts report the actual gasUsed. Etherscan and block explorers display this for every transaction, letting you validate your local measurements against mainnet reality.
The eth_estimateGas RPC method gives a pre-flight estimate, though it adds a safety margin and may differ from the real execution cost.
CI Gas Regression Gates
Wire forge snapshot --check into continuous integration. It fails the build if any test's gas exceeds the committed snapshot beyond a tolerance.
This prevents accidental gas regressions from slipping into production and makes gas a first-class quality metric.
$ forge snapshot --check
# exits non-zero if gas increased vs committed snapshotA Measurement Workflow
A solid gas workflow:
- Write tests covering the hot paths
- Record a baseline with
forge snapshot - Make one optimization at a time
- Run
forge snapshot --diffto confirm the gain - Gate regressions in CI with
--check
Discipline beats cleverness.
Quick Check
Which Foundry command produces a per-function table of min, average, and max gas usage?
Recap
You learned to measure gas:
forge test --gas-reportfor per-function tablesforge snapshot --diffto track changesgasleft()for fine-grained measurement- Verbose traces reveal where gas goes
- Gate regressions in CI with
--check
This completes the Gas Optimization course. Next: the Foundry toolkit in depth.
Perguntas Frequentes
A aula “Medição de gas” é grátis?
Sim — o texto completo de “Medição de gas” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de Web3 & DApp Development Fundamentals, atualize para CoddyKit PRO. O curso de Web3 & DApp Development Fundamentals inclui 4 aulas no total.
O que vou aprender em “Medição de gas”?
Ferramentas de criação de perfis Você pratica Web3 & DApp Development Fundamentals com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.
Preciso ter experiência prévia para começar Web3 & DApp Development Fundamentals?
Nenhuma experiência prévia é necessária. Web3 & DApp Development Fundamentals no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 4 de 4.
Quanto tempo leva a aula “Medição de gas”?
A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.
Posso escrever e executar código nesta aula de Web3 & DApp Development Fundamentals?
Sim. Cada aula de Web3 & DApp Development Fundamentals inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.