libraries/class-wp-session.php
public function write_data() {
		$option_key = "_wp_session_{$this->session_id}";
		// Only write the collection to the DB if it's changed.
		if ( $this->dirty ) {
			if ( false === get_option( $option_key ) ) {
				add_option( "_wp_session_{$this->session_id}", $this->container, '', 'no' );
				add_option( "_wp_session_expires_{$this->session_id}", $this->expires, '', 'no' );
			} else {
				delete_option( "_wp_session_{$this->session_id}" );
				add_option( "_wp_session_{$this->session_id}", $this->container, '', 'no' );
			}
		}
	}
public function write_data() {
		$option_key = "_wp_session_{$this->session_id}";
		// Only write the collection to the DB if it's changed.
		if ( $this->dirty ) {
			if ( false === get_option( $option_key ) ) {
				add_option( "_wp_session_{$this->session_id}", $this->container, '', 'no' );
				add_option( "_wp_session_expires_{$this->session_id}", $this->expires, '', 'no' );
			} else {
				delete_option( "_wp_session_{$this->session_id}" );
				add_option( "_wp_session_{$this->session_id}", $this->container, '', 'no' );
			}
		}
	}
Write the data from the current session to the data storage system.