Allow configuring LRU cache size in app.toml

[ethanfrey]

Summary

Node operators should be able to configure LRU cache size based on their memory availability

Problem Definition

Storing instances in the LRU will have no effect on the results (still deterministic), but should lower execution time at the cost of increased memory usage. We cannot pick universal parameters for this, so we should allow node operators to set it.

Proposal

There seems to be an app.toml that the node operator can configure some subjective values like halt-height and min-gas-fee or such. Let's add one more value:

[wasm]
lru_size = 10

The default should be 0, which means disabled. This value must be parsed at start and is passed into the wasm.NewKeeper function. We currently have hardcoded the value to 3: https://github.com/cosmwasm/wasmd/blob/master/x/wasm/internal/keeper/keeper.go#L44

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[ethanfrey]

We should also allow configuring gas limit for "smart queries" in the app.toml.

This question was brought up in #22

[ethanfrey]

Note, this is where the custom querier handlers get called in the sdk: https://github.com/cosmos/cosmos-sdk/blob/9a183ffbcc0163c8deb71c7fd5f8089a83e58f05/baseapp/abci.go#L441-L460

This is set somewhere in the ante-handler on deliver: https://github.com/cosmos/cosmos-sdk/blob/master/baseapp/baseapp.go#L519-L522

Context.KVStore will set the gas meter based on the last call to Context.SetGasMeter

Ideally, you will do something like this before running the query:

ctx := ctx.WithGasMeter(sdk.NewGasMeter(cfgDefinedQueryGasLimit))
store := ctx.KVStore(k.storeKey)

Note that we must set the gas limit on the ctx before creating the store.
Also, we should set the wasm gas limit like this:

       gas := gasForContract(ctx)
	res, err := k.wasmer.Execute(codeInfo.CodeHash, params, msgs, prefixStore, gas)
	if err != nil {
		return sdk.Result{}, types.ErrExecuteFailed(err)
	}
	consumeGas(ctx, res.GasUsed)