轉: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 Fredclass 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 的生命週期﹝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，若其中一臺機器記憶體滿了，本方法可以從中找到另一臺可用的機器使用。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 <[email protected]> |// | 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 <[email protected]> |// | 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 <[email protected]> * @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 <[email protected]> * @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; /** * If only using one server; contains ip:port to connect to * * @var string * @access private */ var $_single_sock; /** * Array containing ip:port or array(ip:port, weight) * * @var array * @access private */ var $_servers; /** * Our bit buckets * * @var array * @access private */ var $_buckets; /** * Total # of bit buckets we have * * @var interger * @access private */ var $_bucketcount; /** * # of total servers we have * * @var interger * @access private */ var $_active; // }}} // }}} // {{{ methods // {{{ public functions // {{{ memcached() /** * Memcache initializer * * @param array $args Associative array of settings * * @return mixed * @access public */ function memcached ($args) { $this->set_servers($args['servers']); $this->_debug = $args['debug']; $this->stats = array(); $this->_compress_threshold = $args['compress_threshold']; $this->_persistant = isset($args['persistant']) ? $args['persistant'] : false; $this->_compress_enable = true; $this->_have_zlib = function_exists("gzcompress"); $this->_cache_sock = array(); $this->_host_dead = array(); } // }}} // {{{ add() /** * Adds a key/value to the memcache server if one isn't already set with * that key * * @param string $key Key to set with data * @param mixed $val Value to store * @param interger $exp (optional) Time to expire data at * * @return boolean * @access public */ function add ($key, $val, $exp = 0) { return $this->_set('add', $key, $val, $exp); } // }}} // {{{ decr() /** * Decriment a value stored on the memcache server * * @param string $key Key to decriment * @param interger $amt (optional) Amount to decriment * * @return mixed FALSE on failure, value on success * @access public */ function decr ($key, $amt=1) { return $this->_incrdecr('decr', $key, $amt); } // }}} // {{{ delete() /** * Deletes a key from the server, optionally after $time * * @param string $key Key to delete * @param interger $time (optional) How long to wait before deleting * * @return boolean TRUE on success, FALSE on failure * @access public */ function delete ($key, $time = 0) { if (!$this->_active) return false; $sock = $this->get_sock($key); if (!is_resource($sock)) return false; $key = is_array($key) ? $key[1] : $key; $this->stats['delete']++; $cmd = "delete $key $time "; if(!fwrite($sock, $cmd, strlen($cmd))) { $this->_dead_sock($sock); return false; } $res = trim(fgets($sock)); if ($this->_debug) printf("MemCache: delete %s (%s) ", $key, $res); if ($res == "DELETED") return true; return false; } // }}} // {{{ disconnect_all() /** * Disconnects all connected sockets * * @access public */ function disconnect_all () { foreach ($this->_cache_sock as $sock) fclose($sock); $this->_cache_sock = array(); } // }}} // {{{ enable_compress() /** * Enable / Disable compression * * @param boolean $enable TRUE to enable, FALSE to disable * * @access public */ function enable_compress ($enable) { $this->_compress_enable = $enable; } // }}} // {{{ forget_dead_hosts() /** * Forget about all of the dead hosts * * @access public */ function forget_dead_hosts () { $this->_host_dead = array(); } // }}} // {{{ get() /** * Retrieves the value associated with the key from the memcache server * * @param string $key Key to retrieve * * @return mixed * @access public */ function get ($key) { if (!$this->_active) return false; $sock = $this->get_sock($key); if (!is_resource($sock)) return false; $this->stats['get']++; $cmd = "get $key "; if (!fwrite($sock, $cmd, strlen($cmd))) { $this->_dead_sock($sock); return false; } $val = array(); $this->_load_items($sock, $val); if ($this->_debug) foreach ($val as $k => $v) printf("MemCache: sock %s got %s => %s ", $sock, $k, $v); return $val[$key]; } // }}} // {{{ get_multi() /** * Get multiple keys from the server(s) * * @param array $keys Keys to retrieve * * @return array * @access public */ function get_multi ($keys) { if (!$this->_active) return false; $this->stats['get_multi']++; foreach ($keys as $key) { $sock = $this->get_sock($key); if (!is_resource($sock)) continue; $key = is_array($key) ? $key[1] : $key; if (!isset($sock_keys[$sock])) { $sock_keys[$sock] = array(); $socks[] = $sock; } $sock_keys[$sock][] = $key; } // Send out the requests foreach ($socks as $sock) { $cmd = "get"; foreach ($sock_keys[$sock] as $key) { $cmd .= " ". $key; } $cmd .= " "; if (fwrite($sock, $cmd, strlen($cmd))) { $gather[] = $sock; } else { $this->_dead_sock($sock); } } // Parse responses $val = array(); foreach ($gather as $sock) { $this->_load_items($sock, $val); } if ($this->_debug) foreach ($val as $k => $v) printf("MemCache: got %s => %s ", $k, $v); return $val; } // }}} // {{{ incr() /** * Increments $key (optionally) by $amt * * @param string $key Key to increment * @param interger $amt (optional) amount to increment * * @return interger New key value? * @access public */ function incr ($key, $amt=1) { return $this->_incrdecr('incr', $key, $amt); } // }}} // {{{ replace() /** * Overwrites an existing value for key; only works if key is already set * * @param string $key Key to set value as * @param mixed $value Value to store * @param interger $exp (optional) Experiation time * * @return boolean * @access public */ function replace ($key, $value, $exp=0) { return $this->_set('replace', $key, $value, $exp); } // }}} // {{{ run_command() /** * Passes through $cmd to the memcache server connected by $sock; returns * output as an array (null array if no output) * * NOTE: due to a possible bug in how PHP reads while using fgets(), each * line may not be terminated by a . More specifically, my testing * has shown that, on FreeBSD at least, each line is terminated only * with a . This is with the PHP flag auto_detect_line_endings set * to falase (the default). * * @param resource $sock Socket to send command on * @param string $cmd Command to run * * @return array Output array * @access public */ function run_command ($sock, $cmd) { if (!is_resource($sock)) return array(); if (!fwrite($sock, $cmd, strlen($cmd))) return array(); while (true) { $res = fgets($sock); $ret[] = $res; if (preg_match('/^END/', $res)) break; if (strlen($res) == 0) break; } return $ret; } // }}} // {{{ set() /** * Unconditionally sets a key to a given value in the memcache. Returns true * if set successfully. * * @param string $key Key to set value as * @param mixed $value Value to set * @param interger $exp (optional) Experiation time * * @return boolean TRUE on success * @access public */ function set ($key, $value, $exp=0) { return $this->_set('set', $key, $value, $exp); } // }}} // {{{ set_compress_threshold() /** * Sets the compression threshold * * @param interger $thresh Threshold to compress if larger than * * @access public */ function set_compress_threshold ($thresh) { $this->_compress_threshold = $thresh; } // }}} // {{{ set_debug() /** * Sets the debug flag * * @param boolean $dbg TRUE for debugging, FALSE otherwise * * @access public * * @see memcahced::memcached */ function set_debug ($dbg) { $this->_debug = $dbg; } // }}} // {{{ set_servers() /** * Sets the server list to distribute key gets and puts between * * @param array $list Array of servers to connect to * * @access public * * @see memcached::memcached() */ function set_servers ($list) { $this->_servers = $list; $this->_active = count($list); $this->_buckets = null; $this->_bucketcount = 0; $this->_single_sock = null; if ($this->_active == 1) $this->_single_sock = $this->_servers[0]; } // }}} // }}} // {{{ private methods // {{{ _close_sock() /** * Close the specified socket * * @param string $sock Socket to close * * @access private */ function _close_sock ($sock) { $host = array_search($sock, $this->_cache_sock); fclose($this->_cache_sock[$host]); unset($this->_cache_sock[$host]); } // }}} // {{{ _connect_sock() /** * Connects $sock to $host, timing out after $timeout * * @param interger $sock Socket to connect * @param string $host Host:IP to connect to * @param float $timeout (optional) Timeout value, defaults to 0.25s * * @return boolean * @access private */ function _connect_sock (&$sock, $host, $timeout = 0.25) { list ($ip, $port) = explode(":", $host); if ($this->_persistant == 1) { $sock = @pfsockopen($ip, $port, $errno, $errstr, $timeout); } else { $sock = @fsockopen($ip, $port, $errno, $errstr, $timeout); } if (!$sock) return false; return true; } // }}} // {{{ _dead_sock() /** * Marks a host as dead until 30-40 seconds in the future * * @param string $sock Socket to mark as dead * * @access private */ function _dead_sock ($sock) { $host = array_search($sock, $this->_cache_sock); list ($ip, $port) = explode(":", $host); $this->_host_dead[$ip] = time() + 30 + intval(rand(0, 10)); $this->_host_dead[$host] = $this->_host_dead[$ip]; unset($this->_cache_sock[$host]); } // }}} // {{{ get_sock() /** * get_sock * * @param string $key Key to retrieve value for; * * @return mixed resource on success, false on failure * @access private */ function get_sock ($key) { if (!$this->_active) return false; if ($this->_single_sock !== null) return $this->sock_to_host($this->_single_sock); $hv = is_array($key) ? intval($key[0]) : $this->_hashfunc($key); if ($this->_buckets === null) { foreach ($this->_servers as $v) { if (is_array($v)) { for ($i=0; $i<$v[1]; $i++) $bu[] = $v[0]; } else { $bu[] = $v; } } $this->_buckets = $bu; $this->_bucketcount = count($bu); } $realkey = is_array($key) ? $key[1] : $key; for ($tries = 0; $tries<20; $tries++) { $host = $this->_buckets[$hv % $this->_bucketcount]; $sock = $this->sock_to_host($host); if (is_resource($sock)) return $sock; $hv += $this->_hashfunc($tries . $realkey); } return false; } // }}} // {{{ _hashfunc() /** * Creates a hash interger based on the $key * * @param string $key Key to hash * * @return interger Hash value * @access private */ function _hashfunc ($key) { $hash = 0; for ($i=0; $i<strlen($key); $i++) { $hash = $hash*33 + ord($key[$i]); } return $hash; } // }}} // {{{ _incrdecr() /** * Perform increment/decriment on $key * * @param string $cmd Command to perform * @param string $key Key to perform it on * @param interger $amt Amount to adjust * * @return interger New value of $key * @access private */ function _incrdecr ($cmd, $key, $amt=1) { if (!$this->_active) return null; $sock = $this->get_sock($key); if (!is_resource($sock)) return null; $key = is_array($key) ? $key[1] : $key; $this->stats[$cmd]++; if (!fwrite($sock, "$cmd $key $amt ")) return $this->_dead_sock($sock); stream_set_timeout($sock, 1, 0); $line = fgets($sock); if (!preg_match('/^(d+)/', $line, $match)) return null; return $match[1]; } // }}} // {{{ _load_items() /** * Load items into $ret from $sock * * @param resource $sock Socket to read from * @param array $ret Returned values * * @access private */ function _load_items ($sock, &$ret) { while (1) { $decl = fgets($sock); if ($decl == "END ") { return true; } elseif (preg_match('/^VALUE (S+) (d+) (d+) $/', $decl, $match)) { list($rkey, $flags, $len) = array($match[1], $match[2], $match[3]); $bneed = $len+2; $offset = 0; while ($bneed > 0) { $data = fread($sock, $bneed); $n = strlen($data); if ($n == 0) break; $offset += $n; $bneed -= $n; $ret[$rkey] .= $data; } if ($offset != $len+2) { // Something is borked! if ($this->_debug) printf("Something is borked! key %s expecting %d got %d length ", $rkey, $len+2, $offset); unset($ret[$rkey]); $this->_close_sock($sock); return false; } $ret[$rkey] = rtrim($ret[$rkey]); if ($this->_have_zlib && $flags & MEMCACHE_COMPRESSED) $ret[$rkey] = gzuncompress($ret[$rkey]); if ($flags & MEMCACHE_SERIALIZED) $ret[$rkey] = unserialize($ret[$rkey]); } else { print("Error parsing memcached response "); return 0; } } } // }}} // {{{ _set() /** * Performs the requested storage operation to the memcache server * * @param string $cmd Command to perform * @param string $key Key to act on * @param mixed $val What we need to store * @param interger $exp When it should expire * * @return boolean * @access private */ function _set ($cmd, $key, $val, $exp) { if (!$this->_active) return false; $sock = $this->get_sock($key); if (!is_resource($sock)) return false; $this->stats[$cmd]++; $flags = 0; if (!is_scalar($val)) { $val = serialize($val); $flags |= MEMCACHE_SERIALIZED; if ($this->_debug) printf("client: serializing data as it is not scalar "); } $len = strlen($val); if ($this->_have_zlib && $this->_compress_enable && $this->_compress_threshold && $len >= $this->_compress_threshold) { $c_val = gzcompress($val, 9); $c_len = strlen($c_val); if ($c_len < $len*(1 - COMPRESS_SAVINGS)) { if ($this->_debug) printf("client: compressing data; was %d bytes is now %d bytes ", $len, $c_len); $val = $c_val; $len = $c_len; $flags |= MEMCACHE_COMPRESSED; } } if (!fwrite($sock, "$cmd $key $flags $exp $len $val ")) return $this->_dead_sock($sock); $line = trim(fgets($sock)); if ($this->_debug) { if ($flags & MEMCACHE_COMPRESSED) $val = 'compressed data'; printf("MemCache: %s %s => %s (%s) ", $cmd, $key, $val, $line); } if ($line == "STORED") return true; return false; } // }}} // {{{ sock_to_host() /** * Returns the socket for the host * * @param string $host Host:IP to get socket for * * @return mixed IO Stream or false * @access private */ function sock_to_host ($host) { if (isset($this->_cache_sock[$host])) return $this->_cache_sock[$host]; $now = time(); list ($ip, $port) = explode (":", $host); if (isset($this->_host_dead[$host]) && $this->_host_dead[$host] > $now || isset($this->_host_dead[$ip]) && $this->_host_dead[$ip] > $now) return null; if (!$this->_connect_sock($sock, $host)) return $this->_dead_sock($host); // Do not buffer writes stream_set_write_buffer($sock, 0); $this->_cache_sock[$host] = $sock; return $this->_cache_sock[$host]; } // }}} // }}} // }}}}// }}}?>