/**
* @return bool
*/
public function valid()
{
$size = self::$db->size($this->name());
if ($this->position < $this->buffer_position || $this->position >= $this->buffer_position + $size) {
$this->buffer_position = intval($this->position / $size) * $size;
$this->buffer = self::$db->getIndexes($this->name(), $this->buffer_position, $size);
}
return isset($this->buffer[$this->position - $this->buffer_position]);
}
