php导致内存溢出

在执行一个导出csv脚步时，当要导出的数据超过3w多条时，就会报错，如下：

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

php存储3w多条数据这个数组占用内存超过20M

解决方法：分批取数据，分批处理数据
问题点：一次取多少数据最合适
一次取1w条，减少数据库IO操作次数，但php数组就好较大
一次取1k条，增加了数据库IO操作次数，php数组很小

数据一共41000条
因为是循环查询数据，只能返回空，所以会有一次无效的IO查询

综合考虑，觉得使用每次请求1w条数据

代码简单记录下

$filename = '测试';
$head  = array('申请时间', '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操作类

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;
}

/**
* 实例化服务类
* @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;
}

/**
* 拼接要导出的数据
* @param $data
*/
public function sendDate($data) {

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

$
27df
this->content .= implode(",", $temp) . PHP_EOL; //用英文逗号分开
unset($temp);
}
}

/**
* 输出数据
*/
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;
}

}