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tlc: General two level cache (lrucache + shared dict)

Installation

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CentOS/RHEL 6, 7, 8 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua-resty-tlc

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-tlc v0.2 released on Oct 03 2016.


Two Layer Cache implementation using lua-resty-lrucache and shared dictionaries.

Cache entries are written to lru-cache in the current worker and to a shared dictionary.

Cache reads that miss in the worker's lru-cache instance are re-populated from the shared dictionary if available.

Values in shared dictionaries are automatically serialised and unserialised to JSON (custom serialisation functions are supported)

Also provides a manager module to maintain global set of TLC cache instances

Overview

lua_shared_dict tlc_cache 10m;
lua_shared_dict tlc_cache2 1m;

init_by_lua_block {
    local manager = require("resty.tlc.manager")
    manager.new("my_cache", {size = 500, dict = "tlc_cache"})

    manager.new("my_cache2", {size = 500, dict = "tlc_cache2"})
}


location = /get {
    content_by_lua_block {
        local manager = require("resty.tlc.manager")
        local cache = manager.get("my_cache")

        local args = ngx.req.get_uri_args()
        local key = args["key"]

        local data, err = cache:get(key)
        if err then
            ngx.log(ngx.ERR, err)
        elseif data == nil then
            ngx.status = ngx.HTTP_NOT_FOUND
            ngx.say("Not Found")
        else
            ngx.say(tostring(data))
        end
    }
}

location = /set {
    content_by_lua_block {
        local manager = require("resty.tlc.manager")
        local cache = manager.get("my_cache")

        local args = ngx.req.get_uri_args()
        local key = args["key"]
        local val = args["val"] or { foo = bar }
        local ttl = args["ttl"]

        local ok, err = cache:set(key, val, ttl)
        if not ok then
            ngx.log(ngx.ERR, err)
        end
    }
}

location = /flush {
    content_by_lua_block {
        local manager = require("resty.tlc.manager")
        local cache = manager.get("my_cache")
        cache:flush()
    }
}

location = /list {
    content_by_lua_block {
        local manager = require("resty.tlc.manager")
        local instances = manager.list()

        ngx.say(require("cjson").encode(instances))
    }
}

Methods

manager

new

syntax: ok, err = manager.new(name, opts)

Create a new resty.tlc.cache instance with given name/id and options.

Will not check if instance already exists, existing instances will be overwritten

get

syntax: cache = manager.get(name)

Returns the specified TLC cache instance or nil

delete

syntax: manager.delete(name)

Removes the specified cache instance.

list

syntax: instances = manager.list()

Returns an array table of available cache instances

cache

new

syntax: instance = cache:new(opts)

Creates a new instance of resty.tlc.cache, opts is a table of options for this instance.

opts = {
    dict         = dict,         -- Shared dictionary name, required
    size         = size,         -- max_items parameter for LRU cache, optional, default 200
    pureffi      = pureffi,      -- Use the pureffi LRU cache variant, optional, default false
    loadfactor   = loadfactor,   -- Load factor for pureffi LRU cache, optional
    serialiser   = serialiser,   -- Function to serialise values when saving to shared dictionary, optional, defaults to pcall'd cjson encode
    unserialiser = unserialiser, -- Function to unserialise values when saving to shared dictionary, optional, defaults to pcall'd cjson decode
}

Functions to serialise and unserialise should return nil, err on failure.

set

syntax: ok, err = cache:set(key, value, ttl?)

Set or update an entry in the cache.

ttl is optional and in seconds

get

syntax: data = cache:get(key)

Returns data from cache or nil if not set

delete

syntax: cache:delete(key)

Deletes entry from both LRU cache and shared dictionary

TODO: Delete from LRU cache in all workers

flush

syntax: cache:flush(hard?)

Re-initialises LRU cache in current worker and flushes shared dictionary.

hard argument will also call flush_expired() on dictionary.

TODO: Re-initialise LRU cache in all workers

TODO

  • Add feature to ngx_lua shared dictionary to retrieve remaining TTL of entry
  • Syncronise LRU cache delete / flush across workers

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-tlc.

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