Call local_storage_set only in offline context

substrate/frame/merkle-mountain-range/src/mmr/storage.rs

@@ -58,7 +58,11 @@ impl OffchainStorage {
 
 	#[cfg(feature = "runtime-benchmarks")]
 	fn set(key: &[u8], value: &[u8]) {
-		sp_io::offchain::local_storage_set(StorageKind::PERSISTENT, key, value);
+		if sp_io::offchain::is_offchain_db_ext_available() {
+			sp_io::offchain::local_storage_set(StorageKind::PERSISTENT, key, value);
+		} else {
+			sp_io::offchain_index::set(key, value);
+		}
 	}
 }
 

substrate/primitives/io/src/lib.rs

@@ -1343,6 +1343,11 @@ sp_externalities::decl_extension! {
 /// These functions are being made available to the runtime and are called by the runtime.
 #[runtime_interface]
 pub trait Offchain {
+	/// Checks if the offchain database extension is available.
+	fn is_offchain_db_ext_available(&mut self) -> bool {
+		self.extension::<OffchainDbExt>().is_some()
+	}
+
 	/// Returns if the local node is a potential validator.
 	///
 	/// Even if this function returns `true`, it does not mean that any keys are configured