karmacoma-eth / gas-benchmark-anvil

a little foundry template that shows how to use anvil to run gas benchmarks

Running Gas Benchmarks with Anvil

Let's say we want to get an accurate estimate of how much it will cost end users to send Counter.increment() transactions.

Solution

# in one terminal run:
anvil

# in another, run:
forge script script/Counter.s.sol --rpc-url anvil --broadcast

In the output, look for these lines:

# this is the deploy transaction
Paid: 0.00034828536331071 ETH (106719 gas * 3.26357409 gwei)

# this is the increment transaction
Paid: 0.000140232322572324 ETH (43404 gas * 3.230861731 gwei)

From that output we can see that it would cost an end-user exactly 43404 gas to send an increment transaction. This includes the intrinsic gas cost of sending a transaction, as well as calldata costs.

Discussion

Tests don't measure this:

forge test --gas-report
...
[PASS] testIncrement() (gas: 28334)
...
| Function Name                    | min             | avg   | median | max   | # calls |
| increment                        | 22340           | 22340 | 22340  | 22340 | 1       |
...

The 28334 in testIncrement() measure how much it costs to run the test, which includes:

• loading the counter variable from storage
• invoking the contract
• dispatching to the expected function
• executing the function
• running assertEq(counter.number(), 1), which involves doing the same work for another contract call

So for our purpose, the gas score of of testIncrement() includes things we don't want to measure, and does not include the costs associated with an actual transaction (intrinsic cost, calldata cost)

The gas report for increment only includes the gas cost of running that function, which is useful to test optimizations but for our purposes it includes too little.