Remove all blocks with id *

Hi,
I'm developing a mini game and want to reset the world after the game.
Players can only build sandstone, so how can I remove (or replace with air) all the sandstone in the world?

PHP:

$lv = $this->getServer()->getLevelByName("yourworld");
for ($x = -999; $x <= 1000; $x++){
 for ($y = 1; $y <= 100; $y++){
  for ($z = -999; $z <= 100; $z++){
    if ($lv->getBlockIdAt($x,$y,$z) == Item::SANDSTONE){ //no matter which sandstone you build
     $lv->setBlock(new Vector3($x,$y,$z), Block::get(0));
    }
   }
  }
 }


This will lag your server for 20 minutes, so it isn't good way

Or, use WorldResetting method. Backup your worlds at specified folder and then copy the region files

or if it is map generated by plugin or pocketmine you can simply generate new map with the same seed

Or just don't let the world save.

Any example?

/save-off

after

PHP:

if($this->getServer()->isLevelLoaded(/*LevelName*/)){
$this->getServer()->unloadLevel(/*levelname*/);
}
if(!$this->getServer()->isLevelLoaded(/*LevelName*/)){
$this->getServer()->loadLevel(/*LevelName*/);
}


world become back again

Hmm.. You cant cancel levelsaveevent

And only unloading them doesn't work either. Is there something like save-off for plugins? ->saveOff or so?

look how PocketMine does it