PHP对象数组不是线性缩放而全局数组吗？答案

【问题标题】：PHP object array's not linearly scale while global arrays do?PHP对象数组不是线性缩放而全局数组吗？
【发布时间】：2012-05-30 02:24:20
【问题描述】：

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，它以 stdClass 作为节点存储越来越大的数组，运行两个测试，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;
}

还有令人震惊的结果：

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，对象数组属性的扩展速度非常惊人，有时当数组变大时需要 3 到 4 倍的时间，但标准全局数组变量并非如此。

关于这个问题的任何想法或答案，这是否可能是 PHP 引擎的错误？

【问题讨论】：

怀疑这是一个数组问题，但它可能是 OOP 开销，因为您在对象内构建该数组 - 很多 OOP 开销。如果您用标准全局变量临时替换该对象成员，性能是否会发生变化？
能否请您将这个问题简化为实际问题，将整个 prggmr 的东西排除在外？这使问题难以理解。
@MarcB 有变化，但不是重大变化（将历史更改为仅存储真实的$this->_event_history[] = [true] 在 10 秒内每秒产生 9532 个。@NikiC 你有什么建议吗？修剪一下？
不过，您仍在使用对象内数组。试试global $history; $history[] = ...。
@MarcB 我的错误读错了评论，似乎用全局变量替换它确实提供了与没有事件历史记录的运行几乎相同的结果......所以我猜这个问题真的在对象数组中变得可行不是线性缩放的？

标签： php scalability

【解决方案1】：

我在 PHP 5.3.9 上测试了您的代码。为此，我必须将[] 转换为array()，并且我还必须更正您的第12 行：从$a=new MyTest($size) 到$mytest=new MyTest($size)（顺便说一句，构造函数参数被默默地忽略，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一个unset($mytest);（以获得更一致的内存日志），并且还将您的 5000000 替换为 1000000，因为我只有 2GB 的 RAM .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，在函数调用中附加到数组的成本几乎与在原始方法调用中执行它一样多（并且具有相同的非线性行为）。有一件事可以肯定地说：

是函数调用占用了 CPU 时间！

关于非线性行为，它只有在某个阈值以上才会变得非常明显。虽然所有三种情况都具有相同的内存行为（由于不完整的 gargabe 收集，这仅在本日志中的“普通数组”和“函数内部数组”情况下很明显），它是“方法内部数组”和“函数内的数组”具有相同执行时间行为的情况。这意味着函数调用本身会导致时间的非线性增加。在我看来可以这样说：

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）并获得以下输出：

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。另请注意，这三种情况的执行时间差异如何不如以前那么明显。请记住，最里面的操作在所有情况下都是相同的。

我不会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，对这里的每个人和我自己也是如此.

【讨论】：

另外，如果你不添加 unset($mytest);，一切都会慢 10%。
这里的答案很好......这确实需要深入研究 php 源代码，因为在我看来，在访问它们的上下文之间的变量时发生了一些事情，导致使用时间大幅减少并考虑它们只是指针和引用（是吗？不应该是吗？）数据的大小应该无关紧要，因为除了添加的附加数据之外没有任何内容被写入......或者这可能只是一次相遇开发人员在开发语言时做出的一些决定可能被忽视了......

【解决方案2】：

我不能在评论中发布这一切，所以这更像是一个观察而不是一个答案。看起来 SplObjectStorage 相当慢。另外，array_push 比 $array[] = 'item';

免责声明：为草率的代码道歉:)

<?php

$time = microtime();
$time = explode(' ', $time);
$time = $time[1] + $time[0];
$start = $time;

$iteration = 10000;

switch ($_REQUEST['test'])
{
    case 1:
        $s = new SplObjectStorage();

        for ($i = 0; $i < $iteration; $i++) {
            $obj = new stdClass;
            $s[$obj] = 'test';
        }
        break;
    case 2:

        $s = array();
        for ($i = 0; $i < $iteration; $i++) {
            $obj = new stdClass;
            $s[$i] = $obj;
        }
        break;

    case 3:
        class Test {
            public $data = array();
        }
        $s = new Test;
        for ($i = 0; $i < $iteration; $i++) {
            $obj = new stdClass;
            $s->data[] = $obj;
        }
        break;

    case 4:
        class Test {
            public static $data = array();
        }
        $s = new Test;
        for ($i = 0; $i < $iteration; $i++) {
            $obj = new stdClass;
            $s->data[] = $obj;
        }
        break;  
    case 5:
        class Test {
            public $data = array();
        }
        $s = new Test;
        for ($i = 0; $i < $iteration; $i++) {
            $obj = new stdClass;
            array_push($s->data, $obj);
        }
        break;  
    default:
        echo 'Type in ?test=#';
}

$time = microtime();
$time = explode(' ', $time);
$time = $time[1] + $time[0];
$finish = $time;
$total_time = round(($finish - $start), 6);
echo 'Page generated in '.$total_time.' seconds.';

【讨论】：

我想知道这个被否决的原因，似乎是一个合理的答案。
@AlixAxel：可能是因为它不是答案。我没有反对，因为看起来代码对于探索 PHP 特性很有用。