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cip 24
title Versioned Gas Scheduler Variables
description Transition to hard fork-only updates for gas scheduler variables
author Nina Barbakadze (@ninabarbakadze)
discussions-to https://forum.celestia.org/t/cip-versioned-gas-scheduler-variables/1785
status Final
type Standards Track
category Core
created 2024-07-24

Abstract

Gas scheduler parameters blob.GasPerBlobByte and auth.TxSizeCostPerByte will no longer be modifiable by governance but may only change via a hard fork upgrade.

Motivation

Versioning on-chain governance modifiable parameters blob.GasPerBlobByte and auth.TxSizeCostPerByte, aims to stabilize gas estimation by removing block-to-block variability. This allows for hardcoding these values into estimators, simplifying the gas estimation process and making transaction costs more predictable without the need for pre-transaction queries.

Specification

Currently, GasPerBlobByte and TxSizeCostPerByte are module parameters within the blob and auth modules, allowing for their modification via ParameterChangeProposal. The proposed modification changes these parameters to hardcoded constants within the application, accessible via version-specific getters.

Parameters

The proposal makes these two variables modifiable through hard fork upgrades:

Previously:

  1. blob.GasPerBlobByte
  2. auth.TxSizeCostPerByte

Now:

  1. appconsts.GasPerBlobByte
  2. appconsts.TxSizeCostPerByte

Backwards Compatibility

Enabling this feature requires a hard fork network upgrade.

Test Cases

Test cases should verify that gas scheduler variables are exclusively updated via hard forks, effectively preventing updates through governance mechanisms and that the gas meter uses those constants.

Reference Implementation

Starting from v3, we updated the PayForBlobs() function in x/blob/keeper.go to use versioned GasPerBlobByte parameter when calculating gas based on the size of the blobs while maintaining compatibility with previous versions.

-       gasToConsume := types.GasToConsume(msg.BlobSizes, k.GasPerBlobByte(ctx))
+       // GasPerBlobByte is a versioned param from version 3 onwards.
+       var gasToConsume uint64
+       if ctx.BlockHeader().Version.App <= v2.Version {
+               gasToConsume = types.GasToConsume(msg.BlobSizes, k.GasPerBlobByte(ctx))
+       } else {
+               gasToConsume = types.GasToConsume(msg.BlobSizes, appconsts.GasPerBlobByte(ctx.BlockHeader().Version.App))
+       }
+

Additionally, we modified the PFB gas estimation logic to use appconsts.DefaultTxSizeCostPerByte.

-// DefaultEstimateGas runs EstimateGas with the system defaults. The network may change these values
-// through governance, thus this function should predominantly be used in testing.
+// DefaultEstimateGas runs EstimateGas with the system defaults.
 func DefaultEstimateGas(blobSizes []uint32) uint64 {
-       return EstimateGas(blobSizes, appconsts.DefaultGasPerBlobByte, auth.DefaultTxSizeCostPerByte)
+       return EstimateGas(blobSizes, appconsts.DefaultGasPerBlobByte, appconsts.DefaultTxSizeCostPerByte)
 }

We also needed to update the gas consumption logic related to transaction size in the ante handler. The AnteHandle function within NewConsumeGasForTxSizeDecorator has been modified to retrieve the TxSizeCostPerByte value from app constants for versions v3 and later. The logic for earlier versions remains unchanged.

+// consumeGasForTxSize consumes gas based on the size of the transaction.
+// It uses different parameters depending on the app version.
+func consumeGasForTxSize(ctx sdk.Context, txBytes uint64, params auth.Params) {
+       // For app v2 and below we should get txSizeCostPerByte from auth module
+       if ctx.BlockHeader().Version.App <= v2.Version {
+               ctx.GasMeter().ConsumeGas(params.TxSizeCostPerByte*txBytes, "txSize")
+       } else {
+               // From v3 onwards, we should get txSizeCostPerByte from appconsts
+               txSizeCostPerByte := appconsts.TxSizeCostPerByte(ctx.BlockHeader().Version.App)
+               ctx.GasMeter().ConsumeGas(txSizeCostPerByte*txBytes, "txSize")
+       }
+}

Security Considerations

This change prioritizes network stability and predictability but requires heightened vigilance against potential misconfigurations.

Copyright

Copyright and related rights waived via CC0.