Enable non-sequential block finalization.

substrate/client/api/src/backend.rs

@@ -551,6 +551,7 @@ pub trait Backend<Block: BlockT>: AuxStore + Send + Sync {
 		&self,
 		hash: Block::Hash,
 		justification: Option<Justification>,
+		ensure_sequential_finalization: bool,
 	) -> sp_blockchain::Result<()>;
 
 	/// Append justification to the block with the given `hash`.

substrate/client/api/src/in_mem.rs

@@ -712,6 +712,7 @@ impl<Block: BlockT> backend::Backend<Block> for Backend<Block> {
 		&self,
 		hash: Block::Hash,
 		justification: Option<Justification>,
+		_ensure_sequesntial_finalization: bool,
 	) -> sp_blockchain::Result<()> {
 		self.blockchain.finalize_header(hash, justification)
 	}

substrate/client/db/src/lib.rs

@@ -1380,10 +1380,13 @@ impl<Block: BlockT> Backend<Block> {
 		justification: Option<Justification>,
 		current_transaction_justifications: &mut HashMap<Block::Hash, Justification>,
 		remove_displaced: bool,
+		ensure_sequential_finalization: bool,
 	) -> ClientResult<MetaUpdate<Block>> {
 		// TODO: ensure best chain contains this block.
 		let number = *header.number();
-		self.ensure_sequential_finalization(header, last_finalized)?;
+		if ensure_sequential_finalization {
+			self.ensure_sequential_finalization(header, last_finalized)?;
+		}
 		let with_state = sc_client_api::Backend::have_state_at(self, hash, number);
 
 		self.note_finalized(
@@ -1481,6 +1484,7 @@ impl<Block: BlockT> Backend<Block> {
 				justification,
 				&mut current_transaction_justifications,
 				finalized_blocks.peek().is_none(),
+				true,
 			)?);
 			last_finalized_hash = block_hash;
 			last_finalized_num = *block_header.number();
@@ -2114,6 +2118,7 @@ impl<Block: BlockT> sc_client_api::backend::Backend<Block> for Backend<Block> {
 		&self,
 		hash: Block::Hash,
 		justification: Option<Justification>,
+		ensure_sequential_finalization: bool,
 	) -> ClientResult<()> {
 		let mut transaction = Transaction::new();
 		let header = self.blockchain.expect_header(hash)?;
@@ -2127,6 +2132,7 @@ impl<Block: BlockT> sc_client_api::backend::Backend<Block> for Backend<Block> {
 			justification,
 			&mut current_transaction_justifications,
 			true,
+			ensure_sequential_finalization,
 		)?;
 
 		self.storage.db.commit(transaction)?;

substrate/client/service/src/client/client.rs

@@ -128,6 +128,10 @@ where
 	fn clear_block_gap(&self) -> sp_blockchain::Result<()> {
 		self.backend.blockchain().clear_block_gap()
 	}
+
+	fn finalize_block(&self, hash: Block::Hash) -> sp_blockchain::Result<()> {
+		self.backend.finalize_block(hash, None, false)
+	}
 }
 
 /// Used in importing a block, where additional changes are made after the runtime

substrate/client/service/src/lib.rs

@@ -106,6 +106,9 @@ pub struct RpcHandlers(Arc<RpcModule<()>>);
 pub trait ClientExt<Block: BlockT, B: backend::Backend<Block>> {
 	/// Clear block gap after initial block insertion.
 	fn clear_block_gap(&self) -> sp_blockchain::Result<()>;
+
+	/// Finalize block disabling sequential order check.
+	fn finalize_block(&self, hash: Block::Hash) -> sp_blockchain::Result<()>;
 }
 
 impl RpcHandlers {

substrate/primitives/blockchain/src/backend.rs

@@ -17,7 +17,7 @@
 
 //! Substrate blockchain trait
 
-use log::warn;
+use log::{debug, warn};
 use parking_lot::RwLock;
 use sp_runtime::{
 	generic::BlockId,
@@ -289,9 +289,14 @@ pub trait Backend<Block: BlockT>:
 					match finalized_chain.iter().rev().nth(distance_from_finalized as usize) {
 						Some(header) => (header.number, header.hash),
 						None => {
-							let header = self.header_metadata(
-								finalized_chain.front().expect("Not empty; qed").parent,
-							)?;
+							let parent = finalized_chain.front().expect("Not empty; qed").parent;
+							let header = match self.header_metadata(parent) {
+								Ok(header) => header,
+								Err(_) => {
+									debug!("Can't find obtain header metatadata: {parent:?}");
+									break;
+								},
+							};
 							let result = (header.number, header.hash);
 							finalized_chain.push_front(header);
 							result