为什么不同的测试顺序会得到不同的结果

Question

我改变了测试顺序，得到了不同的结果。我尝试禁用操作码缓存，添加未设置，但仍然得到不同的结果。为什么?

http://snipplr.com/view/759/

$time_start = microtime(true);
$myArray = array();
for ( $i = 0; $i < 100000; ++$i )
{
   $myArray[] = $i;
   $myArray[] = 'test a string';
}
$time_end = microtime(true);
printf("Took %f seconds for array[]n", $time_end - $time_start);
$time_start = microtime(true);
$myArray = array();
for ( $i = 0; $i < 100000; ++$i )
{
   array_push($myArray, $i);
   array_push($myArray, 'test a string');
}
$time_end = microtime(true);
printf("Took %f seconds for array_pushn", $time_end - $time_start);

耗时0.145872秒for array[]耗时0.154502秒for array_push

$time_start = microtime(true);
$myArray = array();
for ( $i = 0; $i < 100000; ++$i )
{
   array_push($myArray, $i);
   array_push($myArray, 'test a string');
}
$time_end = microtime(true);
printf("Took %f seconds for array_pushn", $time_end - $time_start);
$time_start = microtime(true);
$myArray = array();
for ( $i = 0; $i < 100000; ++$i )
{
   $myArray[] = $i;
   $myArray[] = 'test a string';
}
$time_end = microtime(true);
printf("Took %f seconds for array[]n", $time_end - $time_start);

为array_push花了0.197076秒为array花了0.122565秒[]

将测试次数增加到500000:

for array[] for array_push

为array_push花了1.008018秒为array花了0.494230秒[]

看看我是否改变了测试顺序。2倍的速度差

Answer 1

我的想法是关于内存使用:我添加了memory_get_usage()差异的回声(就像时间一样)，看到了这个:

Took 0.108744 seconds for array_push
memory: 32497848
Took 0.151069 seconds for array_push
memory: 320

和

Took 0.061715 seconds for array[]
memory: 32499584
Took 0.058831 seconds for array[]
memory: -40

so: array_push()似乎没有清理为脚本分配的内存，而array[]似乎这样做了。php需要一些时间来分配新的内存(我猜)，所以array[]之后的array_push()不需要花时间，但array_push()之后的array[]做。

或者，可能是谵妄

ps:所以，为了提高性能，必须调用一个消耗大量内存并且在脚本开始时不清理的函数?!% |