PHP实现读写分离

网上看到一篇文件，内容是讲PHP实现更新数据库和查询数据库分开不同的连接。

主要特性：
1. 简单的读写分离
2. 一个主数据库，可以添加更多的只读数据库
3. 读写分离但不用担心某些特性不支持
4. 缺点：同时连接两个数据库

mysql_rw_php.class.php：

<?php
/****************************************
*** mysql-rw-php version 0.1 @ 2009-4-16
*** code by hqlulu#gmail.com
*** http://www.aslibra.com
*** http://code.google.com/p/mysql-rw-php/
*** code modify from class_mysql.php (uchome)
****************************************/

class mysql_rw_php {
    //查询个数
    var $querynum = 0;
    //当前操作的数据库连接
    var $link = null;
    //字符集
    var $charset;
    //当前数据库
    var $cur_db = '';
    //是否存在有效的只读数据库连接
    var $ro_exist = false;
    //只读数据库连接
    var $link_ro = null;
    //读写数据库连接
    var $link_rw = null;
    
    function mysql_rw_php(){
    }
    
    function connect($dbhost, $dbuser, $dbpw, $dbname = '', $pconnect = 0, $halt = TRUE) {
        if($pconnect) {
            if(!$this->link = @mysql_pconnect($dbhost, $dbuser, $dbpw)) {
                $halt && $this->halt('Can not connect to MySQL server');
            }
        } else {
            if(!$this->link = @mysql_connect($dbhost, $dbuser, $dbpw)) {
                $halt && $this->halt('Can not connect to MySQL server');
            }
        }
        
        //只读连接失败
        if(!$this->link && !$halt) return false;
        
        //未初始化rw时，第一个连接作为rw
        if($this->link_rw == null)
            $this->link_rw = $this->link;
            
        if($this->version() > '4.1') {
            if($this->charset) {
                @mysql_query("SET character_set_connection=$this->charset, character_set_results=$this->charset, character_set_client=binary", $this->link);
            }
            if($this->version() > '5.0.1') {
                @mysql_query("SET sql_mode=''", $this->link);
            }
        }
    
        if($dbname) {
            $this->select_db($dbname);
        }
    }

    //连接一个只读的mysql数据库
    function connect_ro($dbhost, $dbuser, $dbpw, $dbname = '', $pconnect = 0){
        if($this->link_rw == null)
            $this->link_rw = $this->link;
            
        $this->link = null;
        
        //不产生halt错误
        $this->connect($dbhost, $dbuser, $dbpw, $dbname, $pconnect, false);
        if($this->link){
            //连接成功
            //echo "link ro sussess!<br>";
            $this->ro_exist = true;
            $this->link_ro = $this->link;
            if($this->cur_db){
                //如果已经选择过数据库则需要操作一次
                @mysql_select_db($this->cur_db, $this->link_ro);
            }
        }else{
            //连接失败
            //echo "link ro failed!<br>";
            $this->link = &$this->link_rw;
        }
    }
    
    //设置一系列只读数据库并且连接其中一个
    function set_ro_list($ro_list){
        if(is_array($ro_list)){
            //随机选择其中一个
            $link_ro = $ro_list[array_rand($ro_list)];
            $this->connect_ro($link_ro['dbhost'], $link_ro['dbuser'], $link_ro['dbpw']);
        }
    }
    
    function select_db($dbname) {
        //同时操作两个数据库连接
        $this->cur_db = $dbname;
        if($this->ro_exist){
            @mysql_select_db($dbname, $this->link_ro);
        }
        return @mysql_select_db($dbname, $this->link_rw);
    }
    
    function fetch_array($query, $result_type = MYSQL_ASSOC) {
        return mysql_fetch_array($query, $result_type);
    }
    
    function fetch_one_array($sql, $type = '') {
        $qr = $this->query($sql, $type);
        return $this->fetch_array($qr);
    }
    
    function query($sql, $type = '') {
        $this->link = &$this->link_rw;
        //判断是否select语句
        if($this->ro_exist && preg_match ("/^(/s*)select/i", $sql)){
            $this->link = &$this->link_ro;
        }
        $func = $type == 'UNBUFFERED' && @function_exists('mysql_unbuffered_query') ?
                'mysql_unbuffered_query' : 'mysql_query';
        if(!($query = $func($sql, $this->link)) && $type != 'SILENT') {
            $this->halt('MySQL Query Error', $sql);
        }
        $this->querynum++;
        return $query;
    }
    
    function affected_rows() {
        return mysql_affected_rows($this->link);
    }
    
    function error() {
        return (($this->link) ? mysql_error($this->link) : mysql_error());
    }
    
    function errno() {
        return intval(($this->link) ? mysql_errno($this->link) : mysql_errno());
    }
    
    function result($query, $row) {
        $query = @mysql_result($query, $row);
        return $query;
    }
    
    function num_rows($query) {
        $query = mysql_num_rows($query);
        return $query;
    }
    
    function num_fields($query) {
        return mysql_num_fields($query);
    }
    
    function free_result($query) {
        return mysql_free_result($query);
    }
    
    function insert_id() {
        return ($id = mysql_insert_id($this->link)) >= 0 ? $id : $this->result($this->query("SELECT last_insert_id()"), 0);
    }
    
    function fetch_row($query) {
        $query = mysql_fetch_row($query);
        return $query;
    }
    
    function fetch_fields($query) {
        return mysql_fetch_field($query);
    }
    
    function version() {
        return mysql_get_server_info($this->link);
    }
    
    function close() {
        return mysql_close($this->link);
    }
    
    function halt($message = '', $sql = '') {
        $dberror = $this->error();
        $dberrno = $this->errno();
        echo "<div style=/"position:absolute;font-size:11px;font-family:verdana,arial;background:#EBEBEB;padding:0.5em;/">
        <b>MySQL Error</b><br>
        <b>Message</b>: $message<br>
        <b>SQL</b>: $sql<br>
        <b>Error</b>: $dberror<br>
        <b>Errno.</b>: $dberrno<br>
        </div>";
        exit();
    }
}
?>

example.php：

<?php
/****************************************
*** mysql-rw-php version 0.1 @ 2009-4-16
*** code by hqlulu#gmail.com
*** http://www.aslibra.com
*** http://code.google.com/p/mysql-rw-php/
*** code modify from class_mysql.php (uchome)
****************************************/

require_once('mysql_rw_php.class.php');
//rw info
$db_rw = array(
    'dbhost'=>'www.aslibra.com',
    'dbuser'=>'aslibra',
    'dbpw'=>'www.aslibra.com',
    'dbname'=>'test'
);

$db_ro = array(
    array(
        'dbhost'=>'www.aslibra.com:4306',
        'dbuser'=>'aslibra',
        'dbpw'=>'www.aslibra.com'
    )
);

$DB = new mysql_rw_php;

//connect Master
$DB->connect($db_rw[dbhost], $db_rw[dbuser], $db_rw[dbpw], $db_rw[dbname]);

//Method 1: connect one server
$DB->connect_ro($db_ro[0][dbhost], $db_ro[0][dbuser], $db_ro[0][dbpw]);

//Method 2: connect one server from a list by rand
$DB->set_ro_list($db_ro);

//send to rw
$sql = "insert into a set a='test'";
$DB->query($sql);

//send to ro
$sql = "select * from a";
$qr = $DB->query($sql);
while($row = $DB->fetch_array($qr)) {
    echo $row[a];
}
?>