doumiao0498
doumiao0498
2012-05-23 14:04

全局数组的PHP对象数组不是线性扩展吗?

已采纳

There is a major performance issue when using in-object array's as a property versus using a global php array variable, why?

To benchmark this problem I created the following benchmark that stores an increasingly larger array with an stdClass as a node, two tests were run one using an array property in a class the other a global array.

The test code

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;
}

And the shocking results:

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

Now besides the obvious overhead of the object calls itself the object array property scales terribly sometimes taking 3 - 4 times longer when the array becomes larger but this is not the case with the standard global array variable.

Any thoughts or answers regarding this problem and is this a possible bug with the PHP engine?

  • 点赞
  • 写回答
  • 关注问题
  • 收藏
  • 复制链接分享
  • 邀请回答

2条回答

  • douji6940 douji6940 9年前

    I tested your code on PHP 5.3.9. To do so I had to translate [] to array(), and I also had to correct your line #12: from $a=new MyTest($size), to $mytest=new MyTest($size) (BTW, the constructor argument gets silently ignored, funny). I also added this code:

    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());
    }
    

    I added the memory usage line to your loops at the same point, added an unset($mytest); after the object case (to get a more consistent memory log), and also replaced your 5000000's with 1000000's because I only have 2GB of RAM. This is what I got:

    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
    

    As you can see, appending to the array inside a function call costs almost as much as (and has the same non-linear behavior as) doing it inside your original method call. One thing can be said for sure:

    It's the function calls that eat up CPU time!

    Regarding the non-linear behavior, it becomes really evident only above a certain threshold. While all three cases have the same memory behavior (because of incomplete gargabe collection this is only evident among the "plain array" and the "array inside function" case, in this log), it is the "array inside method" and the "array inside function" cases that have the same execution time behavior. This means that it's the function calls themselves that cause a non-linear increase in time. It seems to me that this can be said:

    The amount of data that is around during a function call influences its duration.

    To verify this I replaced all $a[] with $a[0] and all 1000000 with 5000000 (to get similar total execution times) and obtained this output:

    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
    

    Note how the times are almost perfectly linear now. Of course, the array size is stuck to 1 now. Note also how the differences of the execution times of the three cases are less pronounced than before. Remember that the innermost operation is the same in all cases.

    I'm not going to try to fully explain all this (gargabe collection on function call? memory fragmentation? ...?), but I think that I have nonetheless collected some useful information, for everyone here and for myself too.

    点赞 评论 复制链接分享
  • dtyz76562 dtyz76562 9年前

    I can't post this all in a comment, so this is more of an observation than an answer. It looks like SplObjectStorage is fairly slow. Also that array_push is a lot faster than $array[] = 'item';

    Disclaimer: Apologies for the sloppy code :)

    <?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.';
    
    点赞 评论 复制链接分享