资源密集型PHP脚本出现No space left on device (28)错误求助

我有两个PHP脚本，父脚本包含1000000次循环，每次循环通过shell_exec()调用子脚本。子脚本每次调用时向MySQL表插入10000条数据，输出响应后退出，父脚本利用该响应执行后续操作。

脚本已设置为无内存限制和无执行时间限制，多数情况下运行正常，但一段时间后会出现**"No space left on device (28)"**错误。通过phpMyAdmin监控发现：

• 16GB内存中，程序持续占用7GB，缓存内存约6.7GB，空闲内存约160MB；
• CPU使用率稳定在20%左右，连接/进程状态均正常；
• 操作开始前，MySQL表预估约15GB，磁盘剩余空间40GB。

父脚本示例代码 #

<?php
    //parent script
    error_reporting(E_ALL);
    ini_set('max_execution_time', 0);
    ini_set('memory_limit', -1);
    ini_set('max_input_vars', 10000);
    include 'db-connection-script.php';

    for($i =0; $i<1000000; $i++){
        //restart script starting
        $mySqlTableNameEscaped=escapeshellarg($mySqlTableName);

        $cmd = "/usr/bin/php child-script.php $mySqlTableNameEscaped";
        $result = shell_exec($cmd);
        unset($mySqlTableNameEscaped);

        //response taken here
        $resultArray = json_decode($result, true);
        if($resultArray['status'] == "success"){
            $returnArrayFromChildScript = $resultArray['returnArrayFromChildScript'];
            //furthur operations ......
            //......
            //......
        }
        unset($resultArray);
    }
    exit;
?>

子脚本示例代码 #

<?php
    //child script
    error_reporting(E_ALL);
    ini_set('max_execution_time', 0);
    ini_set('memory_limit', -1);
    ini_set('max_input_vars', 10000);
    include 'db-connection-script.php';

    $status = "";
    $returnArrayFromChildScript = array();
    $mySqlTableName = (isset($_SERVER['argv'][1]) AND $_SERVER['argv'][1] != "") ? $_SERVER['argv'][1] : "";

    //mysql operation for selection and insertion of 1000 rows in mySqlTableName sql table is done here.
    //******/
    //******/
    //******/
    //returnArrayFromChildScript[] array is prepared here

    $status = "success";
    echo json_encode( array( 'status' => $status,'returnArrayFromChildScript'=>$returnArrayFromChildScript) ); 
    exit;
?>

内容的提问来源于stack exchange，提问作者Paarth Pratim Mout