[Tile-serving] [openstreetmap/osm2pgsql] Using LuaJIT to speed up lua code (#801)

[mmd]

LuaJIT provides a nice plugin replacement mechanism to run Lua code with JIT optimizations: http://luajit.org/luajit.html.

I did some very quick & dirty prototyping to have at least a working osm2pgsql, and compared run times on a small county extract w/ and w/o LuaJIT.

Before (Lua)
Processing: Node(3045k 1015.2k/s) Way(556k 46.37k/s) Relation(1790 1790.00/s)  parse time: 16s

After (LuaJIT)
Processing: Node(3045k 3045.5k/s) Way(556k 139.12k/s) Relation(3410 3410.00/s)  parse time: 6s

So it seems this might be interesting to be investigated in more detail.

CMake code: https://github.com/ranisalt/forgottenserver/blob/luajit-optional/cmake/FindLuaJIT.cmake

```C++
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0b62652..99887ad 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -85,7 +85,8 @@ find_package(Osmium REQUIRED COMPONENTS io proj)
 include_directories(SYSTEM ${OSMIUM_INCLUDE_DIRS})
 
 if (WITH_LUA)
-  find_package(Lua REQUIRED)
+#  find_package(Lua REQUIRED)
+  find_package(LuaJIT REQUIRED)
   include_directories(${LUA_INCLUDE_DIR})
   set(HAVE_LUA 1)
 endif()
@@ -108,7 +109,7 @@ find_package(Threads)
 
 set (LIBS ${Boost_LIBRARIES} ${PostgreSQL_LIBRARY} ${OSMIUM_LIBRARIES})
 
-if (LUA_FOUND)
+if (LUA_FOUND OR LUAJIT_FOUND)
   list(APPEND LIBS ${LUA_LIBRARIES})
 endif()
 
@@ -212,7 +213,7 @@ set(osm2pgsql_lib_SOURCES
   wkb.hpp
 )
 
-if (LUA_FOUND)
+if (LUA_FOUND OR LUAJIT_FOUND)
   list(APPEND osm2pgsql_lib_SOURCES tagtransform-lua.cpp)
 endif()
 
diff --git a/tagtransform-lua.cpp b/tagtransform-lua.cpp
index cf9021b..a17ed54 100644
--- a/tagtransform-lua.cpp
+++ b/tagtransform-lua.cpp
@@ -19,6 +19,9 @@ lua_tagtransform_t::lua_tagtransform_t(options_t const *options)
   m_extra_attributes(options->extra_attributes)
 {
     luaL_openlibs(L);
+    luaJIT_setmode(L, -1, LUAJIT_MODE_WRAPCFUNC|LUAJIT_MODE_ON);
+    lua_pop(L, 1);
+
     luaL_dofile(L, options->tag_transform_script->c_str());
 
     check_lua_function_exists(m_node_func);
diff --git a/tagtransform-lua.hpp b/tagtransform-lua.hpp
index 0d951ac..de78cd6 100644
--- a/tagtransform-lua.hpp
+++ b/tagtransform-lua.hpp
@@ -6,9 +6,10 @@
 #include "tagtransform.hpp"
 
 extern "C" {
-#include <lua.h>
+#include "luajit.h"
 }
 
+
 class lua_tagtransform_t : public tagtransform_t
 {
 public:
```

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