cli: disable pruning on validators (#3835)

substrate/core/cli/src/lib.rs

@@ -675,13 +675,6 @@ where
 	config.database_path = db_path(&base_path, config.chain_spec.id());
 	config.database_cache_size = cli.database_cache_size;
 	config.state_cache_size = cli.state_cache_size;
-	config.pruning = match cli.pruning {
-		Some(ref s) if s == "archive" => PruningMode::ArchiveAll,
-		None => PruningMode::default(),
-		Some(s) => PruningMode::keep_blocks(s.parse()
-			.map_err(|_| error::Error::Input("Invalid pruning mode specified".to_string()))?
-		),
-	};
 
 	let is_dev = cli.shared_params.dev;
 
@@ -694,6 +687,28 @@ where
 			service::Roles::FULL
 		};
 
+	// by default we disable pruning if the node is an authority (i.e.
+	// `ArchiveAll`), otherwise we keep state for the last 256 blocks. if the
+	// node is an authority and pruning is enabled explicitly, then we error
+	// unless `unsafe_pruning` is set.
+	config.pruning = match cli.pruning {
+		Some(ref s) if s == "archive" => PruningMode::ArchiveAll,
+		None if role == service::Roles::AUTHORITY => PruningMode::ArchiveAll,
+		None => PruningMode::default(),
+		Some(s) => {
+			if role == service::Roles::AUTHORITY && !cli.unsafe_pruning {
+				return Err(error::Error::Input(
+					"Validators should run with state pruning disabled (i.e. archive). \
+					You can ignore this check with `--unsafe-pruning`.".to_string()
+				));
+			}
+
+			PruningMode::keep_blocks(s.parse()
+				.map_err(|_| error::Error::Input("Invalid pruning mode specified".to_string()))?
+			)
+		},
+	};
+
 	config.wasm_method = cli.wasm_method.into();
 
 	let exec = cli.execution_strategies;

substrate/core/cli/src/params.rs

@@ -366,12 +366,22 @@ pub struct RunCmd {
 	#[structopt(long = "rpc-cors", value_name = "ORIGINS", parse(try_from_str = parse_cors))]
 	pub rpc_cors: Option<Cors>,
 
-	/// Specify the pruning mode, a number of blocks to keep or 'archive'.
+	/// Specify the state pruning mode, a number of blocks to keep or 'archive'.
 	///
-	/// Default is 256.
+	/// Default is to keep all block states if the node is running as a
+	/// validator (i.e. 'archive'), otherwise state is only kept for the last
+	/// 256 blocks.
 	#[structopt(long = "pruning", value_name = "PRUNING_MODE")]
 	pub pruning: Option<String>,
 
+	/// Force start with unsafe pruning settings.
+	///
+	/// When running as a validator it is highly recommended to disable state
+	/// pruning (i.e. 'archive') which is the default. The node will refuse to
+	/// start as a validator if pruning is enabled unless this option is set.
+	#[structopt(long = "unsafe-pruning")]
+	pub unsafe_pruning: bool,
+
 	/// The human-readable name for this node.
 	///
 	/// The node name will be reported to the telemetry server, if enabled.