fixed bug in store::clear() - builds batch of delete operations to be…

… applied to the column family

nano/node/rocksdb/rocksdb.cpp

@@ -722,20 +722,20 @@ int nano::rocksdb::store::drop (nano::write_transaction const & transaction_a, t
 
 int nano::rocksdb::store::clear (::rocksdb::ColumnFamilyHandle * column_family)
 {
-	// Dropping completely removes the column
-	auto name = column_family->GetName ();
-	auto status = db->DropColumnFamily (column_family);
-	release_assert (status.ok ());
-
-	// Need to add it back as we just want to clear the contents
-	auto handle_it = std::find_if (handles.begin (), handles.end (), [column_family] (auto & handle) {
-		return handle.get () == column_family;
-	});
-	debug_assert (handle_it != handles.cend ());
-	status = db->CreateColumnFamily (get_cf_options (name), name, &column_family);
-	release_assert (status.ok ());
-	handle_it->reset (column_family);
-	return status.code ();
+	::rocksdb::ReadOptions read_options;
+  ::rocksdb::WriteOptions write_options;
+  ::rocksdb::WriteBatch write_batch;
+  std::unique_ptr<::rocksdb::Iterator> it(db->NewIterator(read_options, column_family));
+
+  for (it->SeekToFirst (); it->Valid (); it->Next ())
+  {
+    write_batch.Delete (column_family, it->key());
+  }
+
+  ::rocksdb::Status status = db->Write(write_options, &write_batch);
+  release_assert(status.ok());
+
+  return status.code();
 }
 
 void nano::rocksdb::store::construct_column_family_mutexes ()