Support for --pruning=auto.

parity/main.rs

@@ -126,11 +126,11 @@ Networking Options:
 
 API and Console Options:
   -j --jsonrpc             Enable the JSON-RPC API server.
+  --jsonrpc-port PORT      Specify the port portion of the JSONRPC API server
+                           [default: 8545].
   --jsonrpc-interface IP   Specify the hostname portion of the JSONRPC API
                            server, IP should be an interface's IP address, or
                            all (all interfaces) or local [default: local].
-  --jsonrpc-port PORT      Specify the port portion of the JSONRPC API server
-                           [default: 8545].
   --jsonrpc-cors URL       Specify CORS header for JSON-RPC API responses
                            [default: null].
   --jsonrpc-apis APIS      Specify the APIs available through the JSONRPC
@@ -169,8 +169,14 @@ Sealing/Mining Options:
 
 Footprint Options:
   --pruning METHOD         Configure pruning of the state/storage trie. METHOD
-                           may be one of: archive, basic (experimental), fast
+                           may be one of auto, archive, basic, fast, light:
-                           (experimental) [default: archive].
+                           archive - keep all state trie data. No pruning.
+                           basic - reference count in disk DB. Slow but light.
+                           fast - maintain journal overlay. Fast but 50MB used.
+                           light - early merges with partial tracking. Fast
+                           and light. Experimental!
+                           auto - use the method most recently synced or
+                           default to archive if none synced [default: auto].
   --cache-pref-size BYTES  Specify the prefered size of the blockchain cache in
                            bytes [default: 16384].
   --cache-max-size BYTES   Specify the maximum size of the blockchain cache in
@@ -536,6 +542,23 @@ impl Configuration {
 		ret
 	}
 
+	fn find_best_db(path: &str) -> Option<journaldb::Algorithm> {
+		let mut ret = None;
+		let mut latest_era = None;
+		for i in [journaldb::Algorithm::Archive, journaldb::Algorithm::EarlyMerge, journaldb::Algorithm::OverlayRecent, journaldb::Algorithm::RefCounted].into_iter() {
+			let db = journaldb::new(path, i);
+			match (latest_era, db.latest_era()) {
+				(Some(best), Some(this)) if best >= this => {}
+				(_, None) => {}
+				(_, Some(this)) => {
+					latest_era = Some(this);
+					ret = Some(i);
+				}
+			}
+		}
+		ret
+	}
+
 	fn client_config(&self) -> ClientConfig {
 		let mut client_config = ClientConfig::default();
 		match self.args.flag_cache {
@@ -553,6 +576,7 @@ impl Configuration {
 			"light" => journaldb::Algorithm::EarlyMerge,
 			"fast" => journaldb::Algorithm::OverlayRecent,
 			"basic" => journaldb::Algorithm::RefCounted,
+			"auto" => Self::find_best_db().unwrap_or(journaldb::Algorithm::OverlayRecent),
 			_ => { die!("Invalid pruning method given."); }
 		};
 		client_config.name = self.args.flag_identity.clone();

util/src/journaldb/archivedb.rs

@@ -168,6 +168,8 @@ impl JournalDB for ArchiveDB {
 		Ok((inserts + deletes) as u32)
 	}
 
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	fn state(&self, id: &H256) -> Option<Bytes> {
 		self.backing.get_by_prefix(&id.bytes()[0..12]).and_then(|b| Some(b.to_vec()))
 	}

util/src/journaldb/earlymergedb.rs

@@ -333,6 +333,8 @@ impl JournalDB for EarlyMergeDB {
 		self.backing.get(&LATEST_ERA_KEY).expect("Low level database error").is_none()
 	}
 
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	fn mem_used(&self) -> usize {
 		self.overlay.mem_used() + match self.refs {
 			Some(ref c) => c.read().unwrap().heap_size_of_children(),

util/src/journaldb/overlayrecentdb.rs

@@ -213,6 +213,8 @@ impl JournalDB for OverlayRecentDB {
 		self.backing.get(&LATEST_ERA_KEY).expect("Low level database error").is_none()
 	}
 
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, H256)>) -> Result<u32, UtilError> {
 		// record new commit's details.
 		trace!("commit: #{} ({}), end era: {:?}", now, id, end);

util/src/journaldb/refcounteddb.rs

@@ -112,6 +112,8 @@ impl JournalDB for RefCountedDB {
 		self.latest_era.is_none()
 	}
 
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, H256)>) -> Result<u32, UtilError> {
 		// journal format:
 		// [era, 0] => [ id, [insert_0, ...], [remove_0, ...] ]
@@ -220,6 +222,25 @@ mod tests {
 		assert!(!jdb.exists(&h));
 	}
 
+	#[test]
+	fn latest_era_should_work() {
+		// history is 3
+		let mut jdb = RefCountedDB::new_temp();
+		assert_eq!(jdb.latest_era(), None);
+		let h = jdb.insert(b"foo");
+		jdb.commit(0, &b"0".sha3(), None).unwrap();
+		assert_eq!(jdb.latest_era(), Some(0));
+		jdb.remove(&h);
+		jdb.commit(1, &b"1".sha3(), None).unwrap();
+		assert_eq!(jdb.latest_era(), Some(1));
+		jdb.commit(2, &b"2".sha3(), None).unwrap();
+		assert_eq!(jdb.latest_era(), Some(2));
+		jdb.commit(3, &b"3".sha3(), Some((0, b"0".sha3()))).unwrap();
+		assert_eq!(jdb.latest_era(), Some(3));
+		jdb.commit(4, &b"4".sha3(), Some((1, b"1".sha3()))).unwrap();
+		assert_eq!(jdb.latest_era(), Some(4));
+	}
+
 	#[test]
 	fn complex() {
 		// history is 1

util/src/journaldb/traits.rs

@@ -31,6 +31,9 @@ pub trait JournalDB : HashDB + Send + Sync {
 	/// Check if this database has any commits
 	fn is_empty(&self) -> bool;
 
+	/// Get the latest era in the DB. None if there isn't yet any data in there.
+	fn latest_era() -> Option<u64> { self.latest_era }
+
 	/// Commit all recent insert operations and canonical historical commits' removals from the
 	/// old era to the backing database, reverting any non-canonical historical commit's inserts.
 	fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, H256)>) -> Result<u32, UtilError>;