PHP没有'；I don’我不能解放我的记忆

我有以下代码，它从数据库接收数据（相当多），并将它们传递给处理这些数据的函数。以下是代码的样子。

for($o=0; $o<$times; $o++)
    {
        echo "Before Data: ".memory_get_peak_usage().PHP_EOL;
        $data = $u->getDataLimit($id, $market, ($o*5000));
        echo "After Data: ".memory_get_peak_usage().PHP_EOL;
        echo "Before Process: ".memory_get_peak_usage().PHP_EOL;
        $feed.= $p->process($data, ($o*5000) , 0, 0);
        echo "After Process: ".memory_get_peak_usage().PHP_EOL;
        $data = null; // or unset($data) doesnt matter.
        echo "After All: ".memory_get_peak_usage().PHP_EOL.PHP_EOL;
    }

这就是输出。

Before Data: 9587976
After Data: 37969952
Before Process: 37969952
After Process: 70166880
After All: 70166928
Before Data: 70166928
After Data: 83876232
Before Process: 83876232
After Process: 118233752
After All: 118233752
Before Data: 118233752
After Data: 141275760
Before Process: 141275760
After Process: 178939696
After All: 178939696
Before Data: 178939696
After Data: 202189192
Before Process: 202189192
After Process: 242915840
After All: 242915840
Before Data: 242915840
PHP Fatal error:  Allowed memory size of 262144000 bytes exhausted (tried to allocate 32 bytes) in /var/www/repricing/repricing/library/Zend/Db/Statement/Pdo.php on line 290

memory_get_usage():的输出

Before Data: 9476792
After Data: 37943024
Before Process: 37969952
After Process: 70182072
After All: 56630760
Before Data: 56630760
After Data: 83864432
Before Process: 83897400
After Process: 118242320
After All: 113905024
Before Data: 113905024
After Data: 141247528
Before Process: 141278200
After Process: 178989656
After All: 174954320
Before Data: 174954320
After Data: 202216704
Before Process: 202251672
After Process: 243004472
After All: 241208824
Before Data: 241208824
PHP Fatal error:  Allowed memory size of 262144000 bytes exhausted (tried to allocate 95 bytes) in /var/www/repricing/repricing/library/Zend/Db/Statement/Pdo.php on line 290

在我看来，PHP并没有释放$data，相反，它只是把它放在首位？$feed只是一个字符串。不是很大。我不明白为什么那个脚本内存不足。以及为什么它不释放数据。