protected function is_queue_empty() {
		global $wpdb;

		$table  = $wpdb->options;
		$column = 'option_name';

		if ( is_multisite() ) {
			$table  = $wpdb->sitemeta;
			$column = 'meta_key';
		}

		$key = $wpdb->esc_like( $this->identifier . '_batch_' ) . '%';

		$count = $wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM {$table} WHERE {$column} LIKE %s", $key ) ); // @codingStandardsIgnoreLine.

		return ! ( $count > 0 );
	}