记遇到的一个php坑

最近对项目的一个高访问量业务接口进行功能扩展，上线一段时间后，服务器cpu load突然飙升，并出现大量502。一开始找运维查看日志，并没有看是什么问题，后来发现别的部门项目之前也遇到类似的问题，原来是触发了一个php bug。此bug触发条件是：PHP版本低于5.6.12、开启opcache、高访问量、定义 const 常量并且为二维数组，刚好满足这些条件，真心泪奔。。升级服务器上面的PHP版本之后，就没有再出现了。重启php-fpm，可以一段时间内不会出现502，应急处理之用。

php bug：https://bugs.php.net/bug.php?id=70601

const
            REPLACEMENTS_PASS_1 = [
        	"\x00" => "", "\x01" => "", "\x02" => "", "\x03" => "", 
		"\x04" => "", "\x05" => "", "\x06" => "", "\x07" => "", 
		"\x08" => "", "\x0B" => "", "\x0C" => "", "\x0D" => "", 
		"\x0E" => "", "\x0F" => "", "\x10" => "", "\x11" => "", 
		"\x12" => "", "\x13" => "", "\x14" => "", "\x15" => "", 
		"\x16" => "", "\x17" => "", "\x18" => "", "\x19" => "", 
		"\x1A" => "", "\x1B" => "", "\x1C" => "", "\x1D" => "", 
		"\x1E" => "", "\x1F" => "", "\x7F" => "",
    ];
	
	public function __construct() {
		echo strtr("abcd", self::REPLACEMENTS_PASS_1);
	}