Reduce booting time by using is_empty method

core/src/scheme/scheme.rs

@@ -249,7 +249,7 @@ impl Scheme {
     }
 
     pub fn check_genesis_root(&self, db: &HashDB) -> bool {
-        if db.keys().is_empty() {
+        if db.is_empty() {
             return true
         }
         db.contains(&self.state_root())

util/hashdb/src/lib.rs

@@ -48,6 +48,9 @@ pub trait HashDB: AsHashDB + Send + Sync {
     /// Remove a datum previously inserted. Insertions can be "owed" such that the same number of `insert()`s may
     /// happen without the data being eventually being inserted into the DB. It can be "owed" more than once.
     fn remove(&mut self, key: &H256);
+
+    /// check if the db has no commits
+    fn is_empty(&self) -> bool;
 }
 
 /// Upcast trait.

util/journaldb/src/archivedb.rs

@@ -102,6 +102,10 @@ impl HashDB for ArchiveDB {
     fn remove(&mut self, key: &H256) {
         self.overlay.remove(key);
     }
+
+    fn is_empty(&self) -> bool {
+        self.latest_era.is_none()
+    }
 }
 
 impl JournalDB for ArchiveDB {
@@ -114,10 +118,6 @@ impl JournalDB for ArchiveDB {
         })
     }
 
-    fn is_empty(&self) -> bool {
-        self.latest_era.is_none()
-    }
-
     fn latest_era(&self) -> Option<u64> {
         self.latest_era
     }

util/journaldb/src/traits.rs

@@ -35,9 +35,6 @@ pub trait JournalDB: HashDB {
         0
     }
 
-    /// Check if this database has any commits
-    fn is_empty(&self) -> bool;
-
     /// Get the earliest era in the DB. None if there isn't yet any data in there.
     fn earliest_era(&self) -> Option<u64> {
         None

util/memorydb/src/lib.rs

@@ -262,6 +262,10 @@ impl HashDB for MemoryDB {
             }
         }
     }
+
+    fn is_empty(&self) -> bool {
+        self.data.is_empty()
+    }
 }
 
 #[cfg(test)]