Extendable gas costs

[alpe]

Gas costs are currently constants in the Code that can not be changed without forking. For example https://github.com/CosmWasm/wasmd/blob/master/x/wasm/keeper/keeper.go#L41

We should not enforce the same costs on every chain that is using this module. Some options are

• Params (create extra gas costs)
• Overwrite via compile time flag on a var
• Abstract provider interface that returns the value

[ethanfrey]

Important to allow this customization.

Overwrite via compile time flag on a var

I would support this as an easy first step. You could override when compiling wasmd, or in the app.go of any chain importing x/wasm. These need to be able to be tuned, but I do not think very often.

Params (create extra gas costs)

This is an important one for any gas costs or limits that need to be adjusted "quickly" with a governance vote without redeploying a new binary. I would reflect carefully on what fields to add to params if it would really be useful (and just use public var for the rest)