php – Memcached缓慢获取,高CPU使用率

我有一个在机器上运行的memcached实例来承担数据库的压力.
目前通过 PHP每秒大约有350个请求,根据memcached文档应该是完全可行的,但是我看到get()次的速度非常慢.平均值约为60 ms,两种方式都有尖峰(0.1 ms和250 ms).

memcached进程也一直使用大约80％的CPU.它变得非常棘手,因为所有组合在一起需要5秒以上才能完成页面.

我很确定这是get命令,因为我已在代码中注释掉并且数据库接管,使memcached进程使用0 CPU.

以下是统计数据：

stats
STAT pid 617
STAT uptime 855901
STAT time 1370358572
STAT version 1.4.5
STAT pointer_size 32
STAT rusage_user 15472.778988
STAT rusage_system 38712.971409
STAT curr_connections 175
STAT total_connections 4423163
STAT connection_structures 252
STAT cmd_get 319670822
STAT cmd_set 48996864
STAT cmd_flush 0
STAT get_hits 233440856
STAT get_misses 86229966
STAT delete_misses 11025386
STAT delete_hits 11131141
STAT incr_misses 27702934
STAT incr_hits 19471007
STAT decr_misses 0
STAT decr_hits 0
STAT cas_misses 0
STAT cas_hits 0
STAT cas_badval 0
STAT auth_cmds 0
STAT auth_errors 0
STAT bytes_read 25484001864
STAT bytes_written 77617943971
STAT limit_maxbytes 201326592
STAT accepting_conns 1
STAT listen_disabled_num 0
STAT threads 4
STAT conn_yields 0
STAT bytes 47135355
STAT curr_items 539471
STAT total_items 21293860
STAT evictions 3183365
STAT reclaimed 3222011
END

和设置：

stats settings
STAT maxbytes 201326592
STAT maxconns 1024
STAT tcpport 11211
STAT udpport 11211
STAT inter 127.0.0.1
STAT verbosity 0
STAT oldest 0
STAT evictions on
STAT domain_socket NULL
STAT umask 700
STAT growth_factor 1.25
STAT chunk_size 48
STAT num_threads 4
STAT stat_key_prefix :
STAT detail_enabled no
STAT reqs_per_event 20
STAT cas_enabled yes
STAT tcp_backlog 1024
STAT binding_protocol auto-negotiate
STAT auth_enabled_sasl no
STAT item_size_max 1048576
END

现在我配置memcached错了吗？或者还有其他事情发生了吗？

编辑：

根据要求,这里是get的代码(它没有多少)：

function getItem($memcached,$key,$id) {
    $md5key = md5($key.":".$id);
    $v = $memcached->get($md5key); // changing this to $v = false made the memcached CPU usage go to 0
    if ($v === false) {
        //code that fetches the correct data for each key,stores it in memcached and in $v.
    }
    return $v;
}

在主脚本中有以下内容：

$memcached = new Memcached;
$memcached->addServer('localhost',11211) or die ("Could not connect to memcached server");
$memcached->setOption(Memcached::OPT_COMPRESSION,false);

$myItem = getItem($memcached,"key","123");

EDIT2：
出于某种原因,我仍然注意到数据库的高负荷.现在,当我通过telnet手动检查缓存中存在的数据时,它很好.可能是memcached客户端认为与缓存的连接超时并因此进入数据库？那会让我想到为什么地球上的连接超时……