第 20 章： Lua 脚本
=======================

创建并修改 Lua 环境
------------------------

服务器与 Lua 环境。

.. graphviz::

    digraph {

        label = "\n图 20-1    服务器状态中的 Lua 环境";

        rankdir = LR;

        node [shape = record];

        server [label = "redisServer | ... | <lua> lua | ...", width = 2.0, height = 2.0];

        lua [label = "Lua 环境", shape = circle];

        server:lua -> lua;

    }


Lua 环境协作组件
-----------------------

Lua 脚本执行 Redis 命令时的通讯步骤。

.. graphviz::

    digraph {

        label = "\n图 20-2    Lua 脚本执行 Redis 命令时的通讯步骤";

        rankdir = LR;

        node [shape = record, height = 2.0];

        splines = polyline;

        //

        lua [label = "L\nu\na\n环\n境"];
        fake_client [label = "伪\n客\n户\n端"];
        eval [label = "命\n令\n执\n行\n器"];

        lua -> fake_client [label = "1) 传送 redis.call 函数\n想要执行的 Redis 命令"]
        fake_client -> eval [label = "2) 将命令传给执行器执行"];
        lua -> fake_client [dir = back, label = "\n4) 将命令结果传回给 Lua 环境"];
        fake_client -> eval [dir = back, label = "\n3) 返回命令的执行结果"];
    }

作为例子，
图 20-3 展示了 Lua 脚本在执行以下命令时：

::

    redis> EVAL "return redis.call('DBSIZE')" 0
    (integer) 10086

Lua 环境、伪客户端、命令执行器三者之间的通讯过程。

.. graphviz::

    digraph {

        label = "\n图 20-3    Lua 脚本执行 DBSIZE 命令时的通讯步骤";

        rankdir = LR;

        node [shape = record, height = 2.0];

        splines = polyline;

        //

        lua [label = "L\nu\na\n环\n境"];
        fake_client [label = "伪\n客\n户\n端"];
        eval [label = "命\n令\n执\n行\n器"];

        lua -> fake_client [label = "1) 传送 DBSIZE 请求"]
        fake_client -> eval [label = "2) 将 DBSIZE 命令传给执行器执行"];
        lua -> fake_client [dir = back, label = "\n4) 将命令结果 10086 传回给 Lua 环境"];
        fake_client -> eval [dir = back, label = "\n3) 返回命令的执行结果 10086"];
    }

----

``lua_scripts`` 字典示例。

.. graphviz::

    digraph {

        label = "\n 图 20-4    lua_scripts 字典示例";
        
        rankdir = LR;

        node [shape = record];

        //

        lua_scripts [label = "lua_scripts | ... | <1> \"2f31ba2bb6d6a0f42cc159d2e2dad55440778de3\" | <2> \"a27e7e8a43702b7046d4f6a7ccf5b60cef6b9bd9\" | <3> \"4475bfb5919b5ad16424cb50f74d4724ae833e72\" | ... "];

        node [shape = plaintext];

        one [label = "\"return 'hi'\""];
        two [label = "\"return 1+1\""];
        three [label = "\"return 2*2\""];

        lua_scripts:1 -> one;
        lua_scripts:2 -> two;
        lua_scripts:3 -> three;
    }


脚本管理命令的实现
----------------------

带有超时处理钩子的脚本的运行过程。

.. graphviz::

    digraph {

        label = "\n图 20-8    带有超时处理钩子的脚本的执行过程";

        node [shape = box];

        start_script [label = "开始执行脚本", width = 3.5];

        finish_or_not [label = "脚本执行完毕？", shape = diamond];

        finish [label = "返回执行结果"];

        overtime_or_not [label = "定期调用钩子\n检查脚本\n是否已超时运行？", shape = diamond];

        kill_or_shutdown_arrive_or_not [label = "有 SCRIPT KILL\n或者\nSHUTDOWN NOSAVE\n到达？", shape = diamond];

        stop_script [label = "执行 SCRIPT KILL \n 或者 SHUTDOWN"];

        keep_running [label = "继续执行脚本"];

        //

        start_script -> finish_or_not;

        finish_or_not -> finish [label = "是"];

        finish_or_not -> overtime_or_not [label = "否"];

        overtime_or_not -> kill_or_shutdown_arrive_or_not [label = "是"];

        overtime_or_not -> keep_running [label = "否"];

        kill_or_shutdown_arrive_or_not -> stop_script [label = "是"];

        kill_or_shutdown_arrive_or_not -> keep_running [label = "否"];

        keep_running -> finish_or_not;

    }


脚本复制
-------------

将脚本命令传播给从服务器。

.. graphviz::

    digraph {

        label = "\n 图 20-9    将脚本命令传播给从服务器";

        rankdir = LR;

        //

        node [shape = circle, width = 1.0];

        client [label = "客户端", width = 1.3];

        master [label = "主服务器", width = 1.3];

        slave1 [label = "从服务器 1"];

        slave2 [label = "从服务器 2"];

        more [label = "...", shape = plaintext];

        slaveN [label = "从服务器 N"];

        //

        edge [label = "EVAL \n 或者 \n SCRIPT FLUSH \n 或者 \n SCRIPT LOAD"];

        client -> master;
        master -> slave1;
        master -> slave2;
        master -> more;
        master -> slaveN;

    }

----

主服务器判断该传播 ``EVAL`` 命令还是 ``EVALSHA`` 命令的流程。

.. graphviz::

    digraph {

        label = "\n 图 20-12    主服务器判断传播 EVAL 还是 EVALSHA 的过程";

        node [shape = box];

        command [label = " 主服务器在本机执行完命令 \n EVALSHA <sha1> <numkeys> [key ...] [arg ...] "];

        sha1_exists_in_scriptcache_or_not [label = "校验和 sha1 是否存在于 \n repl_scriptcache_dict 字典？", shape = diamond];

        propagate_evalsha [label = "传播 \n EVALSHA <sha1> <numkeys> [key ...] [arg ...]"];

        convert_evalsha_to_eval [label = "将 EVALSHA 命令转换成等价的 EVAL 命令"];

        propagate_eval [label = "传播 \n EVAL <script> <numkeys> [key ...] [arg ...]"];

        add_sha1_to_scriptcache [label = "将 sha1 添加到 \n repl_scriptcache_dict 字典"];

        //

        command -> sha1_exists_in_scriptcache_or_not;

        sha1_exists_in_scriptcache_or_not -> propagate_evalsha [label = "是"];

        sha1_exists_in_scriptcache_or_not -> convert_evalsha_to_eval [label = "否"];

        convert_evalsha_to_eval -> propagate_eval;

        propagate_eval -> add_sha1_to_scriptcache;    

    }