转:http://blog.twpug.org/index.php?blogId=30
請注意是 Memcached 不是 mmcache，很多人搞不清楚他們兩個的不同！多半玩過 PHP 的人大概都聽過 mmcache，它是一個預編譯緩衝的 PHP 加速程式，能夠提升 PHP 的執行效能。但很少人聽過 Memcached ，因為大多人乍看之下都以為它是mmcache，使得它沒什麼機會介紹自己。事實上，若您正打算架構一個真正高負載的大型網站系統，你需要了解的並不是 mmcache，而是 memcached。
Memcached 是什麼？顧名思義，他是由記憶體(Memory)和暫存(cache)所組合起來的常駐程式(Daemon)，你也可以稱它為『暫存伺服器』。 Memcached 能提供一個暫存資料的服務，透過網路供其他電腦使用。Memcached 有什麼用途？最常見的應用就是在網站伺服器的叢集，它能讓許多的網站伺服器 Session 互相流通使用。如果你正在傷透腦筋煩惱這一點，恭喜你找到解決方法了！
想要在網站伺服器的叢集中，多網站伺服器 Session 互相流通使用，首先你必須將 Memcached 架起來當 Session 分享伺服器，這邊建議你使用大的記憶體，最好是能多大就有多大，因為 Memcached 並不會以硬碟當資料暫存，而是會完全跑在記憶體上，所以若記憶被用完了，Memcached 就會無法再存放更多資料。
接著，你必須修改 PHP 的 Session Save Handler，讓 PHP 懂得利用 Memcached Server 存放 PHP 的 Session 資料並能從 Memcached Server 取出 Session 的資料。PHP提供了 session_set_save_handler() 函式讓我們能輕易修改 Session Save Handler ，以下是我修改後的 PHP 程式碼，你必須在呼叫 session_start() 之前使用：
require_once
"
memcached-client.php
"
;
define
(
"
SHARED_SESS_TIME
"
,
3600
);
//
Timeout// Session Class by Fred
class
Shared_Session{
function
init() {
ini_set
(
"
session.use_trans_sid
"
,
0
);
ini_set
(
"
session.gc_maxlifetime
"
,
SHARED_SESS_TIME);
ini_set
(
"
session.use_cookies
"
,
1
);
ini_set
(
"
session.cookie_path
"
,
"
/
"
);
ini_set
(
"
session.cookie_domain
"
,
"
.yourdomain.com.tw
"
);
session_module_name
(
"
user
"
);
session_set_save_handler
(
array
(
"
Shared_Session
"
,
"
open
"
)
,
array
(
"
Shared_Session
"
,
"
close
"
)
,
array
(
"
Shared_Session
"
,
"
read
"
)
,
array
(
"
Shared_Session
"
,
"
write
"
)
,
array
(
"
Shared_Session
"
,
"
destroy
"
)
,
array
(
"
Shared_Session
"
,
"
gc
"
) ); }
function
open(
$save_path
,
$session_name
) {
return
true
; }
function
close() {
return
true
; }
function
read(
$sesskey
) {
global
$memcache
;
return
$memcache
->
get(
$sesskey
); }
function
write(
$sesskey
,
$data
) {
global
$memcache
;
$memcache
->
set(
$sesskey
,
$data
,
SHARED_SESS_TIME);
return
true
; }
function
destroy(
$sesskey
) {
global
$memcache
;
$memcache
->
delete(
$sesskey
);
$memcache
->
flush_all();
return
true
; }
function
gc(
$maxlifetime
=
null
) {
return
true
; }}
$GLOBALS
[
"
memcache
"
]
=
new
memcached(
array
(
'
servers
'
=>
array
(
'
127.0.0.1:11212
'
)
,
'
debug
'
=>
false
,
'
compress_threshold
'
=>
10240
,
'
persistant
'
=>
true
));Shared_Session
::
init();
?>
其中粗字體的部分，是要特別修改的地方：
- 3600 是 Session 的生命周期﹝以秒為單位﹞，這應該不用再做太多解釋。
- .yourdomain.com.tw 是你的網域名稱：想像一個情況若是 Loadbalance 在用戶第一次連線分配用戶到A伺服器，第二次連線分配給同一用戶到B伺服器，會導致 B 伺服器無法透過 cookies 取得 A 伺服器分配給用戶的 session_id，因為 cookies 無法跨網域存取，解決方法是必須修改 cookies 的網域設定，讓 www1.yourdomain.com.tw、www2.yourdomain.com.tw、www3.yourdomain.com.tw...等等，都可以共同存取同一個 cookies ，以取得同一個 session_id，故此時你必須設定成為『.yourdomain.com.tw』。
- 192.168.1.1 這是你的 Memcached Server 的 IP 位置，這裡值得提的是 add_server() 方法，你可以有多行設定許多 IP 做 Loadbalance 負載分配，前面也講到 Memcached 是純粹使用記憶體，若其中一台機器記憶體滿了，本方法可以從中找到另一台可用的機器使用。故你可以建立一個 Memcached 的叢集來處理 Session。
附:memcached-client.php
php
//
// +---------------------------------------------------------------------------+// | memcached client, PHP |// +---------------------------------------------------------------------------+// | Copyright (c) 2003 Ryan T. Dean // | All rights reserved. |// | |// | Redistribution and use in source and binary forms, with or without |// | modification, are permitted provided that the following conditions |// | are met: |// | |// | 1. Redistributions of source code must retain the above copyright |// | notice, this list of conditions and the following disclaimer. |// | 2. Redistributions in binary form must reproduce the above copyright |// | notice, this list of conditions and the following disclaimer in the |// | documentation and/or other materials provided with the distribution. |// | |// | THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |// | IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |// | OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |// | IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |// | INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |// | NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |// | DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |// | THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |// | (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |// | THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |// +---------------------------------------------------------------------------+// | Author: Ryan T. Dean // | Heavily influenced by the Perl memcached client by Brad Fitzpatrick. |// | Permission granted by Brad Fitzpatrick for relicense of ported Perl |// | client logic under 2-clause BSD license. |// +---------------------------------------------------------------------------+//// $TCAnet$//
/*
* * This is the PHP client for memcached - a distributed memory cache daemon. * More information is available at http://www.danga.com/memcached/ * * Usage example: * * require_once 'memcached.php'; * * $mc = new memcached(array( * 'servers' => array('127.0.0.1:10000', * array('192.0.0.1:10010', 2), * '127.0.0.1:10020'), * 'debug' => false, * 'compress_threshold' => 10240, * 'persistant' => true)); * * $mc->add('key', array('some', 'array')); * $mc->replace('key', 'some random string'); * $val = $mc->get('key'); * * @author Ryan T. Dean * @package memcached-client * @version 0.1.2
//
{{{ requirements// }}}// {{{ constants// {{{ flags
/*
* * Flag: indicates data is serialized
*/
define
(
"
MEMCACHE_SERIALIZED
"
,
1
<<
0
);
/*
* * Flag: indicates data is compressed
*/
define
(
"
MEMCACHE_COMPRESSED
"
,
1
<<
1
);
//
}}}
/*
* * Minimum savings to store data compressed
*/
define
(
"
COMPRESSION_SAVINGS
"
,
0.20
);
//
}}}// {{{ class memcached
/*
* * memcached client class implemented using (p)fsockopen() * * @author Ryan T. Dean * @package memcached-client
class
memcached{
//
{{{ properties // {{{ public
/*
* * Command statistics * * @var array * @access public
*/
var
$stats
;
//
}}} // {{{ private
/*
* * Cached Sockets that are connected * * @var array * @access private
*/
var
$_cache_sock
;
/*
* * Current debug status; 0 - none to 9 - profiling * * @var boolean * @access private
*/
var
$_debug
;
/*
* * Dead hosts, assoc array, 'host'=>'unixtime when ok to check again' * * @var array * @access private
*/
var
$_host_dead
;
/*
* * Is compression available? * * @var boolean * @access private
*/
var
$_have_zlib
;
/*
* * Do we want to use compression? * * @var boolean * @access private
*/
var
$_compress_enable
;
/*
* * At how many bytes should we compress? * * @var interger * @access private
*/
var
$_compress_threshold
;
/*
* * Are we using persistant links? * * @var boolean * @access private
*/
var
$_persistant
;
/*
*