lua_code_cache
syntax: lua_code_cache on | off
default: lua_code_cache on
context: http, server, location, location if
Enables or disables the Lua code cache for Lua code in *_by_lua_file directives (like set_by_lua_file and
content_by_lua_file and Lua modules.
When turning off, every request served by ngx_lua will run in a separate Lua VM instance, starting from the 0.9.3 release. So the Lua files referenced in set_by_lua_file,
content_by_lua_file, access_by_lua_file,
and etc will not be cached
and all Lua modules used will be loaded from scratch. With this in place, developers can adopt an edit-and-refresh approach.
Please note however, that Lua code written inlined within nginx.conf
such as those specified by set_by_lua, content_by_lua,
access_by_lua, and rewrite_by_lua will not be updated when you edit the inlined Lua code in your nginx.conf file because only the Nginx config file parser can correctly parse the nginx.conf
file and the only way is to reload the config file
by sending a HUP signal or just to restart Nginx.
Even when the code cache is enabled, Lua files which are loaded by dofile or loadfile
in *_by_lua_file cannot be cached (unless you cache the results yourself). Usually you can either use the init_by_lua
or init_by_lua_file directives to load all such files or just make these Lua files true Lua modules
and load them via require.
The ngx_lua module does not support the stat mode available with the
Apache mod_lua module (yet).
Disabling the Lua code cache is strongly discouraged for production use and should only be used during development as it has a significant negative impact on overall performance. For example, the performance a "hello world" Lua example can drop by an order of magnitude after disabling the Lua code cache.
中文
语法: lua_code_cache on | off
默认值: lua_code_cache on
上下文: http, server, location, location if
开启或者关闭lua代码缓存，在*_by_lua_file（如set_by_lua_file和content_by_lua_file）指令和Lua模块中生效。 从0.9.3稳定版开始，当lua_code_cache指令关闭时，所以被ngx_lua解析的请求都将运行在单独的虚拟机实例中。因此，被set_by_lua_file，content_by_lua_file，access_by_lua_file等等引用的Lua文件将不会被缓存，所有lua模块在被使用时都将会被重新读取加载，在这里，开发人员可以编辑刷新即可显示，不需要重启nginx服务。
然而,请注意,当你编辑lua脚本时，那些被写在nginx.conf内部的lua脚本（如set_by_lua，content_by_lua，access_by_lua和rewrite_by_lua引用的脚本）将不会被重新加载，因为只有Nginx配置文件解析器能正确解析nginx.conf配置文件，而且能够重新加载配置文件的方式只有发送HUP信号量和重启Nginx。
甚至当lua代码缓存被开启的时候，这些在*_by_lua_file中通过dofile或者loadfile被加载的lua文件也不能被缓存（除非你自己去缓存他）。通常你能用init_by_lua或者init-by_lua_file指令加载所以这样的文件，或者编译这些lua文件到lua模块通过require加载。
ngx_lua模块任然不支持stat模式。
强烈的不建议在生成环境中关闭lua代码缓存，仅仅在开发期间关闭，因为关闭缓存对整体性能有很大的负面影响。例如在一个hello world的lua示例中关闭代码缓存，性能将下降一个数量级。