lua-tablepool - Lua table recycling pools for LuaJIT
Table of Contents
- Bugs and Patches
- Copyright and License
local tablepool = require "tablepool" local pool_name = "some_tag" local my_tb = tablepool.fetch(pool_name, 0, 10) -- using my_tb for some purposes... tablepool.release(pool_name, my_tb)
This Lua library implements a pool mechanism to recycle small Lua tables. This can avoid frequent allocations and de-allocation of many small Lua tables for temporary use. Recycling tables can also reduce the overhead of garbage collection in general.
The Lua table pools are shared across all the requests handled by the current NGINX
worker process unless
lua_code_cache is turned off in your
To load the
local tablepool = require "tablepool"
syntax: tb = tablepool.fetch(pool_name, narr, nrec)
Fetches a (free) Lua table from the table pool of the specified name
If the pool
does not exist or the pool is empty, simply create a Lua table whose array part has
narr elements and whose hash table part has
syntax: cache, err = tablepool.release(pool_name, tb, [no_clear])
Releases the already used Lua table,
tb, into the table pool named
pool_name. If the specified
table pool does not exist, create it right away.
The caller must not continue using the released Lua table,
tb, after this call. Otherwise
random data corruption is expected.
no_clear parameter specifies whether to clear the contents in the Lua table
tb before putting it into the pool. Defaults to
false, that is, always clearing the Lua table.
If you always initialize all the elements in the Lua table and always use the exactly same number of elements in the Lua table, then you can set this argument to
avoid the overhead of explicit table clearing.
According to the current implementation, for maximum 200 Lua tables can be cached in
an individual pool. We may make this configurable in the future. If the specified table
pool already exceeds its size limit, then the
tb table is subject to garbage collection. This behavior is to avoid potential memory leak due to unbalanced
release method calls.
Large tables requiring clearing
If you always need to clear out the recycled Lua tables, then you should avoid recycling relatively large Lua tables (like those of hundreds or even thousands of elements in a single table). This is because clearing large Lua tables may offset the benefit of recycling tables.
It is recommended to always watch for the
lj_tab_clear function frames in the C-land on-CPU
flame graphs of your busy nginx worker processes.
This Lua library depends on the new
table.clear API functions first introduced since LuaJIT 2.1.
Older versions of LuaJIT or the standard Lua interpreters will not work at all.
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Bugs and Patches
Please report bugs or submit patches by
Yichun "agentzh" Zhang (章亦春) email@example.com, OpenResty Inc.
Copyright and License
This module is licensed under the BSD license.
Copyright (C) 2016-2021, by Yichun "agentzh" Zhang, OpenResty Inc.
All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
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