技巧:PHP开发网站程序代码的优化方法
如何消灭或优化那PHP开发网站程序的代码呢?
这一点上我个人最主要的经验只有两点,一是消除错误的或低效的循环;二是优化数据库查询语句。其实还存在一些其它的优化细节,比如“str_replace比ereg_replace快”、“echo比print快”等等。这些我暂时都放在一边,稍后我会提到用缓存来对付过于频繁的IO。
下面我们将三个功能相同,但程序写法不同的函数的效率(消耗的时间)进行对比。
webjx.php
require_once('Benchmark/Iterate.php');
define('MAX_RUN',100);
$data = array(1, 2, 3, 4, 5);
doBenchmark('v1', $data);
doBenchmark('v2', $data);
doBenchmark('v3', $data);
function doBenchmark($functionName = null, $arr = null)
{
reset($arr);
$benchmark = new Benchmark_Iterate;
$benchmark->run(MAX_RUN, $functionName, $arr);
$result = $benchmark->get();
echo '<br>';
printf("%s ran %d times where average exec time %.5f ms",$functionName,$result['iterations'],$result['mean'] * 1000);
}
function v1($myArray = null) {
// 效率很差的循环
for ($i =0; $i < sizeof($myArray); $i++)
{
echo '<!--' . $myArray[$i] . ' --> ';
}
}
function v2($myArray = null) {
// 效率略有提高
$max = sizeof($myArray);
for ($i =0; $i < $max ; $i++)
{
echo '<!--' . $myArray[$i] . ' --> ';
}
}
function v3($myArray = null){
//最佳效率
echo "<!--", implode(" --> <!--", $myArray), " --> ";
}
?>
程序输出的结果大概是这样的:
v1 ran 100 times where average exec time 0.18400 ms
v2 ran 100 times where average exec time 0.15500 ms
v3 ran 100 times where average exec time 0.09100 ms
可以看到,函数的执行时间变少,效率上升。
函数v1有个很明显的错误,每一次循环的时间,都需要调用sizeof()函数来计算。 函数v2则在循环外把$myArray数组的元素个数存到$max变量中,避免了每次循环都要计算数组的元素个数,所以效率提高了。函数v3的效率最高,利用了现成的函数,避免循环。
这个例子只是给你一个感性的认识,明白什么是相对高效的代码。在实际开发中,我相信会有很多人会迷迷糊糊地写出很多低效率的代码。要把代码写得精炼而高效,恐怕需要时间去锤炼:-) 但这是另一个话题了,我们略过不谈。
数据库应用基本上每个PHP程序都会用到,在实际开发中我发现最影响整个系统效率的就是数据库这部份。至于数据库的优化和数据查询语句的优化,在此限于篇幅不详细讨论。

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