PHP 对象数组不是线性缩放的，而全局数组呢？

标签 php scalability

使用对象内数组作为属性与使用全局 php 数组变量相比存在一个主要的性能问题，为什么？

为了对这个问题进行基准测试，我创建了以下基准测试，它存储一个越来越大的数组，并将 stdClass 作为节点，运行了两个测试，一个使用类中的数组属性，另一个使用全局数组。

测试代码

ini_set('memory_limit', '2250M');
class MyTest {
    public $storage = [];
    public function push(){
        $this->storage[] = [new stdClass()];
    }
}

echo "Testing Objects".PHP_EOL;
for($size = 1000; $size < 5000000; $size *= 2) {
    $start = milliseconds();
    for ($a=new MyTest(), $i=0;$i<$size;$i++) {
        $a->push();
    }
    $end = milliseconds();
    echo "Array Size $size".PHP_EOL;
    echo $end - $start . " milliseconds to perform".PHP_EOL;
}
echo "================".PHP_EOL;
echo "Testing Array".PHP_EOL;
for($size = 1000; $size < 5000000; $size *= 2) {
    $start = milliseconds();
    for ($a=[], $i=0;$i<$size;$i++) {
        $a[] = [new stdClass()];
    }
    $end = milliseconds();
    echo "Array Size $size".PHP_EOL;
    echo $end - $start . " milliseconds to perform".PHP_EOL;
}

以及令人震惊的结果:

Testing Objects
Array Size 1000
2 milliseconds to perform
Array Size 2000
3 milliseconds to perform
Array Size 4000
6 milliseconds to perform
Array Size 8000
12 milliseconds to perform
Array Size 16000
35 milliseconds to perform
Array Size 32000
97 milliseconds to perform
Array Size 64000
246 milliseconds to perform
Array Size 128000
677 milliseconds to perform
Array Size 256000
2271 milliseconds to perform
Array Size 512000
9244 milliseconds to perform
Array Size 1024000
31186 milliseconds to perform
Array Size 2048000
116123 milliseconds to perform
Array Size 4096000
495588 milliseconds to perform
================
Testing Array
Array Size 1000
1 milliseconds to perform
Array Size 2000
2 milliseconds to perform
Array Size 4000
4 milliseconds to perform
Array Size 8000
8 milliseconds to perform
Array Size 16000
28 milliseconds to perform
Array Size 32000
61 milliseconds to perform
Array Size 64000
114 milliseconds to perform
Array Size 128000
245 milliseconds to perform
Array Size 256000
494 milliseconds to perform
Array Size 512000
970 milliseconds to perform
Array Size 1024000
2003 milliseconds to perform
Array Size 2048000
4241 milliseconds to perform
Array Size 4096000
14260 milliseconds to perform

现在，除了对象调用自身的明显开销之外，当数组变大时，对象数组属性的缩放有时会延长 3 到 4 倍，但标准全局数组变量不是这种情况。

关于这个问题的任何想法或答案，这是否是 PHP 引擎的一个可能的错误？

最佳答案

我在 PHP 5.3.9 上测试了您的代码。为此，我必须将 [] 翻译成 array()，而且我还必须更正您的第 12 行:from $a=new MyTest($ size)，到 $mytest=new MyTest($size)(顺便说一句，构造函数参数被默默地忽略了，有趣)。我还添加了这段代码:

echo "================".PHP_EOL;
echo "Testing Function".PHP_EOL;
for($size = 1000; $size < 1000000; $size *= 2) {
    $start = milliseconds();
    for ($a=array(), $i=0;$i<$size;$i++) {
        my_push($a);
    }
    $end = milliseconds();
    echo "Array Size $size".PHP_EOL;
    echo $end - $start . " milliseconds to perform".PHP_EOL;
    echo "memory usage: ".memory_get_usage()." , real: ".memory_get_usage(true).PHP_EOL;
}

function my_push(&$a)
{
   $a[] = array(new stdClass());
}

我在同一点将内存使用行添加到您的循环中，在对象案例之后添加了 unset($mytest); (以获得更一致的内存日志)，并且还替换了您的5000000 和 1000000 因为我只有 2GB 的内存。这是我得到的:

Testing Objects
Array Size 1000
2 milliseconds to perform
memory usage: 1666376 , real: 1835008
Array Size 2000
5 milliseconds to perform
memory usage: 2063280 , real: 2097152
Array Size 4000
10 milliseconds to perform
memory usage: 2857008 , real: 2883584
Array Size 8000
19 milliseconds to perform
memory usage: 4444456 , real: 4718592
Array Size 16000
44 milliseconds to perform
memory usage: 7619392 , real: 8126464
Array Size 32000
103 milliseconds to perform
memory usage: 13969256 , real: 14417920
Array Size 64000
239 milliseconds to perform
memory usage: 26668936 , real: 27262976
Array Size 128000
588 milliseconds to perform
memory usage: 52068368 , real: 52690944
Array Size 256000
1714 milliseconds to perform
memory usage: 102867104 , real: 103546880
Array Size 512000
5452 milliseconds to perform
memory usage: 204464624 , real: 205258752
================
Testing Array
Array Size 1000
1 milliseconds to perform
memory usage: 18410640 , real: 20709376
Array Size 2000
4 milliseconds to perform
memory usage: 18774760 , real: 20709376
Array Size 4000
7 milliseconds to perform
memory usage: 19502976 , real: 20709376
Array Size 8000
13 milliseconds to perform
memory usage: 20959360 , real: 21233664
Array Size 16000
29 milliseconds to perform
memory usage: 23872176 , real: 24379392
Array Size 32000
61 milliseconds to perform
memory usage: 29697720 , real: 30146560
Array Size 64000
124 milliseconds to perform
memory usage: 41348856 , real: 41943040
Array Size 128000
280 milliseconds to perform
memory usage: 64651088 , real: 65273856
Array Size 256000
534 milliseconds to perform
memory usage: 111255536 , real: 111935488
Array Size 512000
1085 milliseconds to perform
memory usage: 204464464 , real: 205258752
================
Testing Function
Array Size 1000
357 milliseconds to perform
memory usage: 18410696 , real: 22544384
Array Size 2000
4 milliseconds to perform
memory usage: 18774768 , real: 22544384
Array Size 4000
9 milliseconds to perform
memory usage: 19503008 , real: 22544384
Array Size 8000
17 milliseconds to perform
memory usage: 20959392 , real: 22544384
Array Size 16000
36 milliseconds to perform
memory usage: 23872208 , real: 24379392
Array Size 32000
89 milliseconds to perform
memory usage: 29697720 , real: 30146560
Array Size 64000
224 milliseconds to perform
memory usage: 41348888 , real: 41943040
Array Size 128000
529 milliseconds to perform
memory usage: 64651088 , real: 65273856
Array Size 256000
1587 milliseconds to perform
memory usage: 111255616 , real: 111935488
Array Size 512000
5244 milliseconds to perform
memory usage: 204464512 , real: 205258752

如您所见，在函数调用中追加到数组的成本几乎与在原始方法调用中追加的成本一样高(并且具有相同的非线性行为)。有一点可以肯定:

消耗 CPU 时间的是函数调用!

关于非线性行为，只有在超过某个阈值时才会变得非常明显。虽然所有这三种情况都具有相同的内存行为(由于垃圾收集不完整，这仅在“普通数组”和“数组内部函数”情况下很明显，在此日志中)，它是“数组内部方法”和“array inside function”具有相同执行时间行为的情况。这意味着是函数调用自身导致时间非线性增加。在我看来，这可以说:

函数调用期间的数据量会影响其持续时间。

为了验证这一点，我将所有 $a[] 替换为 $a[0] 并将所有 1000000 替换为 5000000(以获得相似的总执行时间)并获得此输出:

Testing Objects
Array Size 1000
2 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 2000
4 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 4000
8 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 8000
15 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 16000
31 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 32000
62 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 64000
123 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 128000
246 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 256000
493 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 512000
985 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 1024000
1978 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 2048000
3965 milliseconds to perform
memory usage: 1302672 , real: 1572864
Array Size 4096000
7905 milliseconds to perform
memory usage: 1302672 , real: 1572864
================
Testing Array
Array Size 1000
1 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 2000
3 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 4000
5 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 8000
10 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 16000
20 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 32000
40 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 64000
80 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 128000
161 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 256000
322 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 512000
646 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 1024000
1285 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 2048000
2574 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 4096000
5142 milliseconds to perform
memory usage: 1302464 , real: 1572864
================
Testing Function
Array Size 1000
1 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 2000
4 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 4000
6 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 8000
14 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 16000
26 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 32000
53 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 64000
105 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 128000
212 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 256000
422 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 512000
844 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 1024000
1688 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 2048000
3377 milliseconds to perform
memory usage: 1302464 , real: 1572864
Array Size 4096000
6814 milliseconds to perform
memory usage: 1302464 , real: 1572864

请注意现在时间几乎是完全线性的。当然，数组大小现在固定为 1。还要注意这三种情况的执行时间差异如何比以前更不明显。请记住，最内层的操作在所有情况下都是相同的。

我不打算尝试完全解释所有这些(函数调用时的垃圾收集？内存碎片？...？)，但我认为我仍然收集了一些有用的信息，对这里的每个人，对我自己也是.

关于PHP 对象数组不是线性缩放的，而全局数组呢？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10721618/

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