Struct frame_support::migrations::RemoveStorage

pub struct RemoveStorage<P: Get<&'static str>, S: Get<&'static str>, DbWeight: Get<RuntimeDbWeight>>(/* private fields */);

RemoveStorage is a utility struct used to remove a storage item from a specific pallet.

This struct is generic over three parameters:

• P is a type that implements the Get trait for a static string, representing the pallet’s name.
• S is a type that implements the Get trait for a static string, representing the storage name.
• DbWeight is a type that implements the Get trait for RuntimeDbWeight, providing the weight for database operations.

On runtime upgrade, the on_runtime_upgrade function will clear the storage from the specified storage, logging the number of keys removed. If the try-runtime feature is enabled, the pre_upgrade and post_upgrade functions can be used to verify the storage removal before and after the upgrade.

Examples:

construct_runtime! {
	pub enum Runtime
	{
		System: frame_system = 0,

		SomePallet: pallet_something = 1,

		YourOtherPallets...
	}
};

parameter_types! {
		pub const SomePallet: &'static str = "SomePallet";
		pub const StorageAccounts: &'static str = "Accounts";
		pub const StorageAccountCount: &'static str = "AccountCount";
}

pub type Migrations = (
	RemoveStorage<SomePallet, StorageAccounts, RocksDbWeight>,
	RemoveStorage<SomePallet, StorageAccountCount, RocksDbWeight>,
	AnyOtherMigrations...
);

pub type Executive = frame_executive::Executive<
	Runtime,
	Block,
	frame_system::ChainContext<Runtime>,
	Runtime,
	Migrations
>;

WARNING: RemoveStorage has no guard rails preventing it from bricking the chain if the operation of removing storage for the given pallet would exceed the block weight limit.

If your storage has too many keys to be removed in a single block, it is advised to wait for a multi-block scheduler currently under development which will allow for removal of storage items (and performing other heavy migrations) over multiple blocks (see https://github.com/paritytech/substrate/issues/13690).

Trait Implementations

impl<P: Get<&'static str>, S: Get<&'static str>, DbWeight: Get<RuntimeDbWeight>> OnRuntimeUpgrade for RemoveStorage<P, S, DbWeight>

fn on_runtime_upgrade() -> Weight

See Hooks::on_runtime_upgrade.

fn pre_upgrade() -> Result<Vec<u8>, TryRuntimeError>

See Hooks::pre_upgrade.

fn post_upgrade(_state: Vec<u8>) -> Result<(), TryRuntimeError>

See Hooks::post_upgrade.

fn try_on_runtime_upgrade(checks: bool) -> Result<Weight, TryRuntimeError>

The expected and default behavior of this method is to handle executing pre_upgrade -> on_runtime_upgrade -> post_upgrade hooks for a migration.