本代码是从uchome的代码修改的，是因为要解决uchome的效率而处理的。
封装的方式比较简单，增加了只读数据库连接的接口扩展，不使用只读数据库也不影响原代码使用。
有待以后不断完善。。

为了方便，试试建立了google的一个项目：
http://code.google.com/p/MySQL-rw-php/

希望给有需要的朋友带来帮助。

PHP实现的Mysql读写分离

主要特性：

简单的读写分离
一个主数据库，可以添加更多的只读数据库
读写分离但不用担心某些特性不支持
缺点：同时连接两个数据库
英文比较烂，也写几个字吧

php code for mysql read/write split
feature:
simply rw split
one master,can add more slaves
support all mysql feature
link to the master and slave at the same time

PHP代码：

mysql_rw_php.class.php

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);
}
}
//http://www.knowsky.com/php.asp 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!
”;
$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!
”;
$this->link = &$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 “

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];
}
?>