diff --git a/.gitignore b/.gitignore
index 01ea94f..d002f61 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 # generated by B3D test
-character.b3d.lua
\ No newline at end of file
+character.b3d.lua
+# generated by Lua logfile test
+logfile.test.lua
\ No newline at end of file
diff --git a/Readme.md b/Readme.md
index 53c1b62..4595a64 100644
--- a/Readme.md
+++ b/Readme.md
@@ -10,6 +10,23 @@ No dependencies. Licensed under the MIT License. Written by Lars Mueller aka LMD
 
 Mostly self-documenting code. Mod namespace is `modlib` or `_ml`, containing all variables & functions.
 
+### Persistence
+
+#### Lua Log Files
+
+A data log file based on Lua statements. **Experimental.** High performance. Example from `test.lua`:
+
+```lua
+local logfile = persistence.lua_log_file.new(mod.get_resource"logfile.test.lua", {})
+logfile:init()
+logfile.root = {}
+logfile:rewrite()
+logfile:set_root({a = 1}, {b = 2, c = 3})
+logfile:close()
+logfile:init()
+assert(table.equals(logfile.root, {[{a = 1}] = {b = 2, c = 3}}))
+```
+
 ### Bluon
 
 Binary Lua object notation. **Experimental.** Handling of subnormal numbers (very small floats) may be broken.
diff --git a/init.lua b/init.lua
index 9c7a564..45b68bc 100644
--- a/init.lua
+++ b/init.lua
@@ -50,7 +50,8 @@ for _, file in pairs{
 	"ranked_set",
 	"binary",
 	"b3d",
-	"bluon"
+	"bluon",
+	"persistence"
 } do
 	modules[file] = file
 end
@@ -77,7 +78,7 @@ end
 local load_module, get_resource, loadfile_exports
 modlib = setmetatable({
 	-- TODO bump on release
-	version = 62,
+	version = 63,
 	modname = minetest and minetest.get_current_modname(),
 	dir_delim = rawget(_G, "DIR_DELIM") or "/",
 	_RG = setmetatable({}, {
diff --git a/persistence.lua b/persistence.lua
new file mode 100644
index 0000000..ebdd5d9
--- /dev/null
+++ b/persistence.lua
@@ -0,0 +1,140 @@
+lua_log_file = {}
+local files = {}
+local metatable = {__index = lua_log_file}
+
+-- TODO register on shutdown
+
+function lua_log_file.new(file_path, root)
+    local self = setmetatable({file_path = assert(file_path), root = root}, metatable)
+    files[self] = true
+    return self
+end
+
+function lua_log_file:load()
+    -- Bytecode is blocked by the engine
+    local read = assert(loadfile(self.file_path))
+    local env = {}
+    setfenv(read, env)
+    read()
+    env.R = env.R or {{}}
+    self.reference_count = #env.R
+    self.root = env.R[1]
+    self.references = modlib.table.flip(env.R)
+end
+
+function lua_log_file:open()
+    self.file = io.open(self.file_path, "a+")
+end
+
+function lua_log_file:init()
+    if modlib.file.exists(self.file_path) then
+        self:load()
+        self:_rewrite()
+        self:open()
+        return
+    end
+    self:open()
+    self.root = {}
+    self:_write()
+end
+
+function lua_log_file:log(statement)
+    self.file:write(statement)
+    self.file:write"\n"
+end
+
+function lua_log_file:flush()
+    self.file:flush()
+end
+
+function lua_log_file:close()
+    self.file:close()
+    self.file = nil
+    files[self] = nil
+end
+
+minetest.register_on_shutdown(function()
+    for self in pairs(files) do
+        self.file:close()
+    end
+end)
+
+-- TODO use shorthand notations
+function lua_log_file:dump(value)
+    if value == nil then
+        return "nil"
+    end
+    if value == true then
+        return "true"
+    end
+    if value == false then
+        return "false"
+    end
+    if value ~= value then
+        -- nan
+        return "0/0"
+    end
+    local _type = type(value)
+    if _type == "number" then
+        return ("%.17g"):format(value)
+    end
+    if self.references[value] then
+        return "R[" .. self.references[value] .. "]"
+    end
+    self.reference_count = self.reference_count + 1
+    local reference = self.reference_count
+    self.references[value] = reference
+    local formatted
+    if _type == "string" then
+        formatted = ("%q"):format(value)
+    elseif _type == "table" then
+        local entries = {}
+        for _, value in ipairs(value) do
+            table.insert(entries, self:dump(value))
+        end
+        for key, value in pairs(value) do
+            if type(key) ~= "number" or key % 1 ~= 0 or key < 1 or key > #value then
+                table.insert(entries, "[" .. self:dump(key) .. "]=" .. self:dump(value))
+            end
+        end
+        formatted = "{" .. table.concat(entries, ";") .. "}"
+    else
+        error("unsupported type: " .. _type)
+    end
+    local key = "R[" .. reference .."]"
+    self:log(key .. "=" .. formatted)
+    return key
+end
+
+function lua_log_file:set(table, key, value)
+    table[key] = value
+    if not self.references[table] then
+        error"orphan table"
+    end
+    self:log(self:dump(table) .. "[" .. self:dump(key) .. "]=" .. self:dump(value))
+end
+
+function lua_log_file:set_root(key, value)
+    return self:set(self.root, key, value)
+end
+
+function lua_log_file:_write()
+    self.references = {}
+    self.reference_count = 0
+    self:log"R={}"
+    self:dump(self.root)
+end
+
+function lua_log_file:_rewrite()
+    self.file = io.open(self.file_path, "w+")
+    self:_write()
+    self.file:close()
+end
+
+function lua_log_file:rewrite()
+    if self.file then
+        self.file:close()
+    end
+    self:_rewrite()
+    self.file = io.open(self.file_path, "a+")
+end
\ No newline at end of file
diff --git a/test.lua b/test.lua
index 0531090..f158540 100644
--- a/test.lua
+++ b/test.lua
@@ -192,6 +192,15 @@ test_from_string("#333", 0x333333FF)
 test_from_string("#694269", 0x694269FF)
 test_from_string("#11223344", 0x11223344)
 
+local logfile = persistence.lua_log_file.new(mod.get_resource"logfile.test.lua", {})
+logfile:init()
+logfile.root = {}
+logfile:rewrite()
+logfile:set_root({a = 1}, {b = 2, c = 3})
+logfile:close()
+logfile:init()
+assert(table.equals(logfile.root, {[{a = 1}] = {b = 2, c = 3}}))
+
 -- in-game tests & b3d testing
 local tests = {
 	-- depends on player_api