php導致內存溢出

在執行一個導出csv腳步時，當要導出的數據超過3w多條時，就會報錯，如下：

Allowed memory size of 134217728 bytes exhausted (tried to allocate 20480 bytes)

php存儲3w多條數據這個數組占用內存超過20M

解決方法：分批取數據，分批處理數據
問題點：一次取多少數據最合適
一次取1w條，減少數據庫IO操作次數，但php數組就好較大
一次取1k條，增加了數據庫IO操作次數，php數組很小

數據一共41000條
因為是循環查詢數據，只能返回空，所以會有一次無效的IO查詢

綜合考慮，覺得使用每次請求1w條數據

代碼簡單記錄下

$filename = '測試';
$head  = array('申請時間', '省', '市', '超市品牌');
$field = array('created_time', 'pro_name', 'city_name', 'brand_name');
$csv   = ExportCsvService::getInstance(implode(",", $head), $field, $filename);

$param['limit'] = C('SQL_LIMIT');
$i              = 0;
while (true) {
        $param['current'] = $i + 1;
        $info             = $rainbowservice->get_list($param)['data']['list'];

        if (empty($info)) {
                $csv->end();
                break;
        } else {
                $csv->sendDate($info);
        }
        unset($info);
        $i++;
}

csv操作類

class ExportCsvService
{

    private $content;
    private $filename;
    private $field;
    private static $instance;

    private function __construct($head,$field,$filename)
    {
        $this->field = $field;
        $this->filename = $filename;
        $this->content  = iconv('UTF-8', 'GBK',$head) . PHP_EOL;
    }

    /**
     * 實例化服務類
     * @param $head
     * @param $field
     * @param $filename
     * @return ExportCsvService
     */
    public static function getInstance($head,$field,$filename) {
        if (!self::$instance instanceof self) {
            self::$instance = new self($head,$field,$filename);
        }
        return self::$instance;
    }

    /**
     * 拼接要導出的數據
     * @param $data
     */
    public function sendDate($data) {

        foreach ($data as $key => $value) {
            $temp = [];
            foreach ($this->field as $k) {
                $temp[] = iconv('UTF-8', 'GBK', $value[$k]);
            }

            $this->content .= implode(",", $temp) . PHP_EOL; //用英文逗號分開
            unset($temp);
        }
    }

    /**
     * 輸出數據
     */
    public function end() {
        header("Content-type:text/csv;charset=GBK");
        header("Content-Disposition:attachment;filename=" . $this->filename);
        header('Cache-Control:must-revalidate,post-check=0,pre-check=0');
        header('Expires:0');
        header('Pragma:public');
        echo $this->content;
    }

}