Runs WordPress Upgrade functions.

Upgrades the database if needed during a site update.

function wp_upgrade() {
		global $wp_current_db_version, $wp_db_version, $wpdb;

		$wp_current_db_version = __get_option( 'db_version' );

		// We are up to date. Nothing to do.
		if ( $wp_db_version == $wp_current_db_version ) {
			return;
		}

		if ( ! is_blog_installed() ) {
			return;
		}

		wp_check_mysql_version();
		wp_cache_flush();
		pre_schema_upgrade();
		make_db_current_silent();
		upgrade_all();
		if ( is_multisite() && is_main_site() ) {
			upgrade_network();
		}
		wp_cache_flush();

		if ( is_multisite() ) {
			update_site_meta( get_current_blog_id(), 'db_version', $wp_db_version );
			update_site_meta( get_current_blog_id(), 'db_last_updated', microtime() );
		}

		/**
		 * Fires after a site is fully upgraded.
		 *
		 * @since 3.9.0
		 *
		 * @param int $wp_db_version         The new $wp_db_version.
		 * @param int $wp_current_db_version The old (current) $wp_db_version.
		 */
		do_action( 'wp_upgrade', $wp_db_version, $wp_current_db_version );
	}
endif;

/**
 * Functions to be called in installation and upgrade scripts.
 *
 * Contains conditional checks to determine which upgrade scripts to run,
 * based on database version and WP version being updated-to.
 *
 * @ignore
 * @since 1.0.1
 *
 * @global int $wp_current_db_version The old (current) database version.
 * @global int $wp_db_version         The new database version.
 */
function upgrade_all() {
	global $wp_current_db_version, $wp_db_version;

	$wp_current_db_version = __get_option( 'db_version' );

	// We are up to date. Nothing to do.
	if ( $wp_db_version == $wp_current_db_version ) {
		return;
	}

	// If the version is not set in the DB, try to guess the version.
	if ( empty( $wp_current_db_version ) ) {
		$wp_current_db_version = 0;

		// If the template option exists, we have 1.5.
		$template = __get_option( 'template' );
		if ( ! empty( $template ) ) {
			$wp_current_db_version = 2541;
		}
	}

	if ( $wp_current_db_version