Check if approval voting db is empty on startup (#6219)

* Add approval voting db sanity check

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* add newline back

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* no need for overlay to read

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

polkadot/node/core/approval-voting/src/lib.rs

@@ -378,6 +378,25 @@ impl ApprovalVotingSubsystem {
 	}
 }
 
+// Checks and logs approval vote db state. It is perfectly normal to start with an
+// empty approval vote DB if we changed DB type or the node will sync from scratch.
+fn db_sanity_check(db: Arc<dyn Database>, config: DatabaseConfig) -> SubsystemResult<()> {
+	let backend = DbBackend::new(db, config);
+	let all_blocks = backend.load_all_blocks()?;
+
+	if all_blocks.is_empty() {
+		gum::info!(target: LOG_TARGET, "Starting with an empty approval vote DB.",);
+	} else {
+		gum::debug!(
+			target: LOG_TARGET,
+			"Starting with {} blocks in approval vote DB.",
+			all_blocks.len()
+		);
+	}
+
+	Ok(())
+}
+
 #[overseer::subsystem(ApprovalVoting, error = SubsystemError, prefix = self::overseer)]
 impl<Context: Send> ApprovalVotingSubsystem {
 	fn start(self, ctx: Context) -> SpawnedSubsystem {
@@ -732,6 +751,10 @@ async fn run<B, Context>(
 where
 	B: Backend,
 {
+	if let Err(err) = db_sanity_check(subsystem.db, subsystem.db_config) {
+		gum::warn!(target: LOG_TARGET, ?err, "Could not run approval vote DB sanity check");
+	}
+
 	let mut state = State {
 		session_window: None,
 		keystore: subsystem.keystore,