PHP 文件缓存数组的实现
在一个试验性项目中,我需要从 sqlite3 数据库中随机读取一条记录给用户,要读取的数据表现在有23850条记录,按 skemu 分类,一般每个 skemu 下有 3000多条记录,原先我使用了 sqlite3 的随机查询语句:
$query="SELECT * FROM shiti WHERE skemu = " . intval($kemuid) . " order by random() limit 1";
然后在我现在用的电脑上没有感觉到明显迟延,但当我把服务器换到一个 P4 1.8G 512M内存的机器上运行时,感觉数据读取速度非常慢,需要2、3秒才能读出数据。如果每次用户要取一条随机记录,都执行这样一个随机查询的话,瓶颈将会出现在数据库查询过程中,难以想像这样的性能如何来适应众多用户的同时访问。为此,我考虑减少数据库的查询次数,先把记录 id 取出来放到数组中,然后从中再来随机取一条记录,同时存为文件供以后读取,这样以减少数据库查询的次数。
以下函数实现读出 id 集:
static function getIDs($kemuid) { $cachefile="cache/" . $kemuid . ".cache"; $datas=array(); if (!file_exists($cachefile)||time() < (filemtime($cachefile) + 14400)) //缓存不存在或超过4小时 { global $data; //读取 id 集 $query="SELECT sid FROM shiti WHERE skemu = " . intval($kemuid); $res = $data->query($query); while($r = $data->fetchArray($res)) { $datas[]=$r['sid']; } //写入缓存 file_put_contents($cachefile,serialize($datas)); } else { //读出缓存 $fp = fopen($cachefile,'r');//读 $datas = unserialize(fread($fp,filesize($cachefile)));//反序列化,并赋值 } return $datas; }
<span style="font-family:Arial"><span style="color:#548dd4"><span style="color:#366092">调用它的读取随机记录函数:</span></span></span>
static function getRondam($kemuid) { global $data; $ids=self::getIDs($kemuid); $index=rand(0,count($ids)-1); $id=$ids[$index]; $query="SELECT * FROM shiti WHERE sid = " . intval($id); $res = $data->query($query); $r = $data->fetchArray($res); $r['da']=$s; return $r; }
<span style="font-family:Arial">这样比每次执行随机查询快多了,但是还是要比生成一个HTML缓存要慢一点,但那样需要把更多数据暴露给客户端,或是存储更多缓存,我想这已经是一个比较均衡的方案了。</span>
<span style="font-family:Arial"></span>
<span style="font-family:Arial">这个解决办法的要点在于数组的序列化与反序列化,大家应该很容易看得懂。</span>

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