测量 Gas
性能分析工具
测量 Gas 是 CoddyKit 上的免费 Web3 & DApp Development Fundamentals 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Web3 & DApp Development Fundamentals 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Web3 & DApp Development Fundamentals 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
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.
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常见问题解答
「测量 Gas」课时是免费的吗？
是的 — 「测量 Gas」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Web3 & DApp Development Fundamentals 课程的其余内容，请升级到 CoddyKit PRO。 Web3 & DApp Development Fundamentals 课程共包含 4 节课。
「测量 Gas」这节课中我会学到什么？
性能分析工具 你通过在浏览器中直接运行的动手代码来练习 Web3 & DApp Development Fundamentals，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Web3 & DApp Development Fundamentals 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Web3 & DApp Development Fundamentals 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。
「测量 Gas」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Web3 & DApp Development Fundamentals 课中编写并运行代码吗？
能。每节 Web3 & DApp Development Fundamentals 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。