Gas is a way to measure computational expense of a smart contract execution, including CPU time and storage cost. It's unit is 1, i.e. you can think of it as countable points. Gas consumption is deterministic, so executing the same thing costs the same amount of gas across all hardware and operating systems.
CosmWasm charges gas for Wasm operations, calls to host functions and calls to the Cosmos SDK. CosmWasm gas is different from Cosmos SDK gas as the numbers here are much larger. Since we charge gas for arbitrary user defined operations, we need to charge each Wasm operation individually and cannot group larger tasks together. As a result, the gas values become much larger than in Cosmos SDK even for very fast executions. There is a multiplier to translate between CosmWasm gas and Cosmos SDK. It was measured and set to 100 a while ago and can be adjusted when necessary.
For CosmWasm gas, the target gas consumption is 1 Teragas (10^12 gas) per millisecond. This idea is inspired by NEAR and we encourage you to read their excellent docs on that topic.
In order to meet this target, we execute Argon2 in a test contract (#1120).
This is a CPU and memory intense job that does not call out into the host. At a
constant gas cost per operation of 1 (pre CosmWasm 1.0), this consumed 96837752
gas and took 15ms on our CI system. The ideal cost per operation for this system
is 10**12 / (96837752 / 15): 154898. This is rounded to 150000 for simplicity.
Each machine is different, we know that. But the above target helps us in multiple ways:
- Develop an intuition what it means to burn X gas or how much gas can be used if a block should be executable in e.g. 1 second
- Have a target for adjustments, e.g. when the Wasm runtime becomes faster or slower
- Allow pricing of calls that are not executed in Wasm, such as crypto APIs
- Find significant over or underpricing