diff --git a/src/activeobject.h b/src/activeobject.h
index fe6c08514..71b9df514 100644
--- a/src/activeobject.h
+++ b/src/activeobject.h
@@ -43,7 +43,7 @@ enum ActiveObjectType {
 
 struct ActiveObjectMessage
 {
-	ActiveObjectMessage(u16 id_, bool reliable_=true, std::string data_=""):
+	ActiveObjectMessage(u16 id_, bool reliable_=true, const std::string &data_ = "") :
 		id(id_),
 		reliable(reliable_),
 		datastring(data_)
diff --git a/src/client.cpp b/src/client.cpp
index 7b962cd94..3cea4fbf4 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -57,7 +57,7 @@ extern gui::IGUIEnvironment* guienv;
 Client::Client(
 		IrrlichtDevice *device,
 		const char *playername,
-		std::string password,
+		const std::string &password,
 		MapDrawControl &control,
 		IWritableTextureSource *tsrc,
 		IWritableShaderSource *shsrc,
diff --git a/src/client.h b/src/client.h
index e7fcb597d..c55d7bcd5 100644
--- a/src/client.h
+++ b/src/client.h
@@ -245,7 +245,7 @@ public:
 	Client(
 			IrrlichtDevice *device,
 			const char *playername,
-			std::string password,
+			const std::string &password,
 			MapDrawControl &control,
 			IWritableTextureSource *tsrc,
 			IWritableShaderSource *shsrc,
diff --git a/src/content_cao.cpp b/src/content_cao.cpp
index ac283da88..3aa3bad97 100644
--- a/src/content_cao.cpp
+++ b/src/content_cao.cpp
@@ -1313,7 +1313,7 @@ void GenericCAO::updateTexturePos()
 	}
 }
 
-void GenericCAO::updateTextures(const std::string mod)
+void GenericCAO::updateTextures(const std::string &mod)
 {
 	ITextureSource *tsrc = m_client->tsrc();
 
diff --git a/src/content_cao.h b/src/content_cao.h
index f30e90e21..a0601d692 100644
--- a/src/content_cao.h
+++ b/src/content_cao.h
@@ -200,7 +200,7 @@ public:
 
 	void updateTexturePos();
 
-	void updateTextures(const std::string mod);
+	void updateTextures(const std::string &mod);
 
 	void updateAnimation();
 
diff --git a/src/filecache.h b/src/filecache.h
index f390f71b7..627ab45ed 100644
--- a/src/filecache.h
+++ b/src/filecache.h
@@ -30,7 +30,7 @@ public:
 	/*
 		'dir' is the file cache directory to use.
 	*/
-	FileCache(std::string dir) : m_dir(dir) {}
+	FileCache(const std::string &dir) : m_dir(dir) {}
 
 	bool update(const std::string &name, const std::string &data);
 	bool load(const std::string &name, std::ostream &os);
diff --git a/src/game.cpp b/src/game.cpp
index f584a58ef..198baeca3 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -79,14 +79,15 @@ extern Profiler *g_profiler;
 	Text input system
 */
 
-struct TextDestNodeMetadata : public TextDest {
+struct TextDestNodeMetadata : public TextDest
+{
 	TextDestNodeMetadata(v3s16 p, Client *client)
 	{
 		m_p = p;
 		m_client = client;
 	}
 	// This is deprecated I guess? -celeron55
-	void gotText(std::wstring text)
+	void gotText(const std::wstring &text)
 	{
 		std::string ntext = wide_to_utf8(text);
 		infostream << "Submitting 'text' field of node at (" << m_p.X << ","
@@ -104,13 +105,14 @@ struct TextDestNodeMetadata : public TextDest {
 	Client *m_client;
 };
 
-struct TextDestPlayerInventory : public TextDest {
+struct TextDestPlayerInventory : public TextDest
+{
 	TextDestPlayerInventory(Client *client)
 	{
 		m_client = client;
 		m_formname = "";
 	}
-	TextDestPlayerInventory(Client *client, std::string formname)
+	TextDestPlayerInventory(Client *client, const std::string &formname)
 	{
 		m_client = client;
 		m_formname = formname;
@@ -131,13 +133,13 @@ struct LocalFormspecHandler : public TextDest
 		m_formname = formname;
 	}
 
-	LocalFormspecHandler(std::string formname, Client *client):
+	LocalFormspecHandler(const std::string &formname, Client *client):
 		m_client(client)
 	{
 		m_formname = formname;
 	}
 
-	void gotText(std::wstring message)
+	void gotText(const std::wstring &message)
 	{
 		errorstream << "LocalFormspecHandler::gotText old style message received" << std::endl;
 	}
@@ -1190,7 +1192,7 @@ protected:
 			u16 port,
 			const SubgameSpec &gamespec);
 	bool initSound();
-	bool createSingleplayerServer(const std::string map_dir,
+	bool createSingleplayerServer(const std::string &map_dir,
 			const SubgameSpec &gamespec, u16 port, std::string *address);
 
 	// Client creation
@@ -1780,7 +1782,7 @@ bool Game::initSound()
 	return true;
 }
 
-bool Game::createSingleplayerServer(const std::string map_dir,
+bool Game::createSingleplayerServer(const std::string &map_dir,
 		const SubgameSpec &gamespec, u16 port, std::string *address)
 {
 	showOverlayMessage(wgettext("Creating server..."), 0, 5);
diff --git a/src/map.cpp b/src/map.cpp
index b690ea3b3..3da96e77b 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -1226,7 +1226,8 @@ bool Map::isBlockOccluded(MapBlock *block, v3s16 cam_pos_nodes) {
 /*
 	ServerMap
 */
-ServerMap::ServerMap(std::string savedir, IGameDef *gamedef, EmergeManager *emerge):
+ServerMap::ServerMap(const std::string &savedir, IGameDef *gamedef,
+		EmergeManager *emerge):
 	Map(dout_server, gamedef),
 	settings_mgr(g_settings, savedir + DIR_DELIM + "map_meta.txt"),
 	m_emerge(emerge),
@@ -1936,7 +1937,7 @@ std::string ServerMap::getSectorDir(v2s16 pos, int layout)
 	}
 }
 
-v2s16 ServerMap::getSectorPos(std::string dirname)
+v2s16 ServerMap::getSectorPos(const std::string &dirname)
 {
 	unsigned int x = 0, y = 0;
 	int r;
@@ -1966,7 +1967,7 @@ v2s16 ServerMap::getSectorPos(std::string dirname)
 	return pos;
 }
 
-v3s16 ServerMap::getBlockPos(std::string sectordir, std::string blockfile)
+v3s16 ServerMap::getBlockPos(const std::string &sectordir, const std::string &blockfile)
 {
 	v2s16 p2d = getSectorPos(sectordir);
 
diff --git a/src/map.h b/src/map.h
index ea8dc76d1..90f97db8b 100644
--- a/src/map.h
+++ b/src/map.h
@@ -360,7 +360,7 @@ public:
 	/*
 		savedir: directory to which map data should be saved
 	*/
-	ServerMap(std::string savedir, IGameDef *gamedef, EmergeManager *emerge);
+	ServerMap(const std::string &savedir, IGameDef *gamedef, EmergeManager *emerge);
 	~ServerMap();
 
 	s32 mapType() const
@@ -422,16 +422,14 @@ public:
 	// returns something like "map/sectors/xxxxxxxx"
 	std::string getSectorDir(v2s16 pos, int layout = 2);
 	// dirname: final directory name
-	v2s16 getSectorPos(std::string dirname);
-	v3s16 getBlockPos(std::string sectordir, std::string blockfile);
+	v2s16 getSectorPos(const std::string &dirname);
+	v3s16 getBlockPos(const std::string &sectordir, const std::string &blockfile);
 	static std::string getBlockFilename(v3s16 p);
 
 	/*
 		Database functions
 	*/
 	static Database *createDatabase(const std::string &name, const std::string &savedir, Settings &conf);
-	// Verify we can read/write to the database
-	void verifyDatabase();
 
 	// Returns true if the database file does not exist
 	bool loadFromFolders();
diff --git a/src/mods.cpp b/src/mods.cpp
index 5a7dc6dca..6fce8e93d 100644
--- a/src/mods.cpp
+++ b/src/mods.cpp
@@ -347,7 +347,7 @@ ClientModConfiguration::ClientModConfiguration(const std::string &path):
 #endif
 
 #if USE_CURL
-Json::Value getModstoreUrl(std::string url)
+Json::Value getModstoreUrl(const std::string &url)
 {
 	std::vector<std::string> extra_headers;
 
diff --git a/src/mods.h b/src/mods.h
index c9bd51d99..1e62db54d 100644
--- a/src/mods.h
+++ b/src/mods.h
@@ -146,9 +146,10 @@ public:
 #endif
 
 #if USE_CURL
-Json::Value getModstoreUrl(std::string url);
+Json::Value getModstoreUrl(const std::string &url);
 #else
-inline Json::Value getModstoreUrl(std::string url) {
+inline Json::Value getModstoreUrl(const std::string &url)
+{
 	return Json::Value();
 }
 #endif
diff --git a/src/shader.cpp b/src/shader.cpp
index 79485025b..66f32c9a1 100644
--- a/src/shader.cpp
+++ b/src/shader.cpp
@@ -340,7 +340,7 @@ IWritableShaderSource* createShaderSource(IrrlichtDevice *device)
 /*
 	Generate shader given the shader name.
 */
-ShaderInfo generate_shader(std::string name,
+ShaderInfo generate_shader(const std::string &name,
 		u8 material_type, u8 drawtype,
 		IrrlichtDevice *device, std::vector<ShaderCallback *> &callbacks,
 		const std::vector<IShaderConstantSetterFactory*> &setter_factories,
@@ -525,7 +525,7 @@ void ShaderSource::rebuildShaders()
 }
 
 
-ShaderInfo generate_shader(std::string name, u8 material_type, u8 drawtype,
+ShaderInfo generate_shader(const std::string &name, u8 material_type, u8 drawtype,
 		IrrlichtDevice *device, std::vector<ShaderCallback *> &callbacks,
 		const std::vector<IShaderConstantSetterFactory*> &setter_factories,
 		SourceShaderCache *sourcecache)
diff --git a/src/treegen.cpp b/src/treegen.cpp
index 505954e8e..8bf9619a0 100644
--- a/src/treegen.cpp
+++ b/src/treegen.cpp
@@ -113,7 +113,7 @@ void make_tree(MMVManip &vmanip, v3s16 p0,
 
 // L-System tree LUA spawner
 treegen::error spawn_ltree(ServerEnvironment *env, v3s16 p0,
-		INodeDefManager *ndef, TreeDef tree_definition)
+		INodeDefManager *ndef, const TreeDef &tree_definition)
 {
 	ServerMap *map = &env->getServerMap();
 	std::map<v3s16, MapBlock*> modified_blocks;
diff --git a/src/treegen.h b/src/treegen.h
index 4e6f95e67..8777c369c 100644
--- a/src/treegen.h
+++ b/src/treegen.h
@@ -73,7 +73,7 @@ namespace treegen {
 		TreeDef tree_definition);
 	// Spawn L-systems tree from LUA
 	treegen::error spawn_ltree (ServerEnvironment *env, v3s16 p0, INodeDefManager *ndef,
-		TreeDef tree_definition);
+		const TreeDef &tree_definition);
 
 	// L-System tree gen helper functions
 	void tree_node_placement(MMVManip &vmanip, v3f p0,