监视器
======================

通过执行 :ref:`MONITOR` 命令，
客户端可以将自己变为一个监视器，
实时地接收并打印出服务器当前处理的命令请求的相关信息：

::

    redis> MONITOR
    OK
    1378822099.421623 [0 127.0.0.1:56604] "PING"
    1378822105.089572 [0 127.0.0.1:56604] "SET" "msg" "hello world"
    1378822109.036925 [0 127.0.0.1:56604] "SET" "number" "123"
    1378822140.649496 [0 127.0.0.1:56604] "SADD" "fruits" "Apple" "Banana" "Cherry"
    1378822154.117160 [0 127.0.0.1:56604] "EXPIRE" "msg" "10086"
    1378822257.329412 [0 127.0.0.1:56604] "KEYS" "*"
    1378822258.690131 [0 127.0.0.1:56604] "DBSIZE"

每当一个客户端向服务器发送一条命令请求时，
服务器除了会处理这条命令请求之外，
还会将关于这条命令请求的信息发送给所有监视器，
如图 24-1 所示。

.. graphviz::

    digraph {

        label = "\n 图 24-1    命令的接收和信息的发送";

        rankdir = LR;

        server [label = "服\n务\n器", shape = box, height = 3.0, width = 1.0];

        node [shape = circle, width = 1.3];

        client [label = "客户端"];

        m1 [label = "监视器 1"];
        m2 [label = "监视器 2"];
        m3 [label = "监视器 3"];

        client -> server [label = "发送命令请求"];

        edge [label = "发送命令信息"];

        server -> m1;
        server -> m2;
        server -> m3;

    }