Ubuntu 10.10 Desktop下安装了Memcached，后来写了一个php文件来测试Memcache：
<?php
$mem = new Memcache;
$mem->connect('127.0.0.1',11211);
$mem->delete('key');
?>
结果在delete的时候老是报错：
coinsight@insight-ubuntu:~$ php clear.php
PHP Notice: MemcachePool::delete(): Server 127.0.0.1 (tcp 11211, udp 0)
failed with: CLIENT_ERROR bad command line format. Usage: delete <key> [noreply]
(0) in /home/coinsight/clear.php on line 4
coinsight@insight-ubuntu:~$
查找了半天原因发现在delete后面加个参数就可以了，而且这个参数必须是0，其它的值同样报错：
<?php
$mem = new Memcache;
$mem->connect('127.0.0.1',11211);
$mem->delete('key',0);
?>
后来百度+GG找，原因如下：
nibblebot at gmail dot com 09-Jul-2010 03:58
the Memcache::delete(key) function is broken on several combinations of memcached+pecl-memcache combinations.
pecl-memcache 2.2.5 + memcached 1.4.2 - Memcache::delete(key) WORKS
pecl-memcache 2.2.5 + memcached 1.4.3 - Memcache::delete(key) DOES NOT WORK
pecl-memcache 2.2.5 + memcached 1.4.4 - Memcache::delete(key) WORKS
pecl-memcache 2.2.5 + memcached 1.4.5 - Memcache::delete(key) WORKS
pecl-memcache 3.0.4 + memcached 1.4.2 - Memcache::delete(key) WORKS
pecl-memcache 3.0.4 + memcached 1.4.3 - Memcache::delete(key) DOES NOT WORK
pecl-memcache 3.0.4 + memcached 1.4.4 - Memcache::delete(key) DOES NOT WORK
pecl-memcache 3.0.4 + memcached 1.4.5 - Memcache::delete(key) DOES NOT WORK
解决方案：(1)手动安装对应的版本 (2)在delete函数里面多加一个参数0。