Begin logging queries to the specified connection and logging key.
If the specified logging key is already running this method does nothing.
$logging_key: The identification key for this log request. By specifying different logging keys we are able to start and stop multiple logging runs simultaneously without them colliding.
public function start($logging_key) {
if (empty($this->queryLog[$logging_key])) {
$this
->clear($logging_key);
}
}