Forked Parity pallet, didn't migrate storage, deployed to chain. How to clear original storage from the live chain?

Question

We started a chain using pallet_collator_selection and later forked it. Both the original and the forked pallet use the LastAuthoredBlock StorageItem. We did not execute a storage migration from the original to the forked pallet.

The storage docs state that a storage key is made up of the pallet name and the item name, implying that our forked pallet actually created its own storage key hash(forked_collator_selection)hash(LastAuthoredBlock) instead of reusing hash(pallet_collator_selection)hash(LastAuthoredBlock), rendering the latter unused memory.

Is there a way to free the memory of the old, now unreferenced hash(pallet_collator_selection)hash(LastAuthoredBlock) StorageItem on the live chain after the forked pallet has been deployed without migrating storage at the time?

Corollary question to: Reclaim used space of a removed StorageItem on a live chain

Answer 1

You can use remove_storage_prefix:

remove_storage_prefix("OldPalletNameInYourRuntime", "LastAuthoredBlock", &[]);

You need to place this into a runtime migration. The last parameter hash is empty here because you don't have a map here (the function is generic over storage items and maps).

Or you could also send a transaction to your chain kill_storage. Be aware that this call requires root. As argument you pass a vector with the only element being the raw key of the old storage item (hash(pallet_collator_selection)hash(LastAuthoredBlock)).