Gas Snapshots

Kythera can generate gas snapshots for all your test functions. This can be useful to get a general feel for how much gas your contract will consume, or to compare gas usage before and after various optimizations.

To generate the gas snapshot, run kythera snapshot <Path to artifacts>.

This will generate a file called .gas-snapshot by default with all your tests and their respective gas usage.

$ kythera snapshot ./artifacts
$ cat .gas-snapshot

name,cost,passed
Basic.wasm::TestConstructorSetup,1519299,true
Basic.wasm::TestMethodParameter,2707176,true
Basic.wasm::TestFailed,1306487,false
Basic.wasm::TestFailFailed,1229328,false
Basic.wasm::TestFailSuccess,1306503,true

The format of the file is a CSV file containing three columns:

• name: identifier of the method for the given CSV line, in the format <Actor name>.wasm::<Method name>.
• cost: gas cost to run the test method.
• passed: boolean representing if the test was successful or not.

Comparing gas usage #

If you would like to compare the current snapshot file with your latest changes, you can use the --diff or --check options.

--diff will compare against the snapshot and display changes from the snapshot.

It can also optionally take a file name (--diff <FILE_NAME>), with the default being .gas-snapshot.

For example:

$ kythera snapshot ./artifacts --diff

Basic.t.wasm: testing 5 tests

Generating gas snapshot
Basic.wasm::TestConstructorSetup: gas used is 0% more
Basic.wasm::TestMethodParameter: gas used is the same: 2707176
Basic.wasm::TestFailed: gas used is 6% less
Basic.wasm::TestFailFailed: gas used is the same: 1229328
Basic.wasm::TestFailSuccess: gas used is the same: 1306503
Total gas dif: -77111

--check will execute the exact same logic but will exit with an exit code 1 if a difference is found.