Database errors when running WordPress on Google App Engine

I’m trying to run WordPress on my PHP runtime whitelisted Google App Engine application. I created a module named “wordpress” and installed WordPress 3.6.1 (in Dutch) as per the instructions found in this article. (Update: I tried WordPress 2.5.1 English, 2.6 Dutch and 2.6.1 Dutch. I got the same error messages with all versions.)

It worked without a problem in my local development environment but not in production on Google App Engine. When I go to http://www.mydomain.com/wordpress/, it redirects to http://www.mydomain.com/wordpress/wp-admin/install.php. In the App Engine logs of the WordPress module I get these messages (“databasefout” means “database error”):

E 2013-10-02 09:23:33.030
WordPress databasefout Table 'wordpress_db.wp_options' doesn't exist bij query SELECT option_value FROM wp_options WHERE option_name = 'siteurl' LIMIT 1 gemaakt door require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), wp_plugin_directory_constants, get_option
...
E 2013-10-02 09:23:33.506
WordPress databasefout Table 'wordpress_db.wp_options' doesn't exist bij query SELECT option_value FROM wp_options WHERE option_name = 'cron' LIMIT 1 gemaakt door require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), do_action('init'), call_user_func_array, wp_schedule_update_checks, wp_next_scheduled, _get_cron_array, get_option
E 2013-10-02 09:23:33.511
WordPress databasefout Table 'wordpress_db.wp_options' doesn't exist bij query INSERT INTO `wp_options` (`option_name`, `option_value`, `autoload`) VALUES ('cron', 'a:2:{i:1380698613;a:1:{s:16:"wp_version_check";a:1:{s:32:"40cd750bba9870f18aada2478b24840a";a:3:{s:8:"schedule";s:10:"twicedaily";s:4:"args";a:0:{}s:8:"interval";i:43200;}}}s:7:"version";i:2;}', 'yes') ON DUPLICATE KEY UPDATE `option_name` = VALUES(`option_name`), `option_value` = VALUES(`option_value`), `autoload` = VALUES(`autoload`) gemaakt door require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), do_action('init'), call_user_func_array, wp_schedule_update_checks, wp_schedule_event, _set_cron_array, update_option, add_option
E 2013-10-02 09:23:33.513
WordPress databasefout Table 'wordpress_db.wp_options' doesn't exist bij query UPDATE `wp_options` SET `option_value` = 'a:2:{i:1380698613;a:2:{s:16:"wp_version_check";a:1:{s:32:"40cd750bba9870f18aada2478b24840a";a:3:{s:8:"schedule";s:10:"twicedaily";s:4:"args";a:0:{}s:8:"interval";i:43200;}}s:17:"wp_update_plugins";a:1:{s:32:"40cd750bba9870f18aada2478b24840a";a:3:{s:8:"schedule";s:10:"twicedaily";s:4:"args";a:0:{}s:8:"interval";i:43200;}}}s:7:"version";i:2;}' WHERE `option_name` = 'cron' gemaakt door require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), do_action('init'), call_user_func_array, wp_schedule_update_checks, wp_schedule_event, _set_cron_array, update_option
E 2013-10-02 09:23:33.515
WordPress databasefout Table 'wordpress_db.wp_options' doesn't exist bij query UPDATE `wp_options` SET `option_value` = 'a:2:{i:1380698613;a:3:{s:16:"wp_version_check";a:1:{s:32:"40cd750bba9870f18aada2478b24840a";a:3:{s:8:"schedule";s:10:"twicedaily";s:4:"args";a:0:{}s:8:"interval";i:43200;}}s:17:"wp_update_plugins";a:1:{s:32:"40cd750bba9870f18aada2478b24840a";a:3:{s:8:"schedule";s:10:"twicedaily";s:4:"args";a:0:{}s:8:"interval";i:43200;}}s:16:"wp_update_themes";a:1:{s:32:"40cd750bba9870f18aada2478b24840a";a:3:{s:8:"schedule";s:10:"twicedaily";s:4:"args";a:0:{}s:8:"interval";i:43200;}}}s:7:"version";i:2;}' WHERE `option_name` = 'cron' gemaakt door require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), do_action('init'), call_user_func_array, wp_schedule_update_checks, wp_schedule_event, _set_cron_array, update_option
E 2013-10-02 09:23:33.516
WordPress databasefout Table 'wordpress_db.wp_options' doesn't exist bij query SELECT option_value FROM wp_options WHERE option_name = 'theme_switched' LIMIT 1 gemaakt door require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), do_action('init'), call_user_func_array, check_theme_switched, get_option
E 2013-10-02 09:23:33.518
WordPress databasefout Table 'wordpress_db.wp_options' doesn't exist bij query SELECT option_value FROM wp_options WHERE option_name = 'rewrite_rules' LIMIT 1 gemaakt door require('wp-blog-header.php'), wp, WP->main, WP->parse_request, WP_Rewrite->wp_rewrite_rules, get_option
...
E 2013-10-02 09:23:33.530
WordPress databasefout Table 'wordpress_db.wp_options' doesn't exist bij query SELECT option_value FROM wp_options WHERE option_name = 'sticky_posts' LIMIT 1 gemaakt door require('wp-blog-header.php'), wp, WP->main, WP->query_posts, WP_Query->query, WP_Query->get_posts, get_option

My database wordpress_db on my Google Cloud SQL instance is still empty (no tables). My MySQL user has the following privileges:

GRANTEE
TABLE_CATALOG
TABLE_SCHEMA
PRIVILEGE_TYPE
IS_GRANTABLE
'wp_user'@'localhost'
def
wordpress_db
SELECT
NO
'wp_user'@'localhost'
def
wordpress_db
INSERT
NO
'wp_user'@'localhost'
def
wordpress_db
UPDATE
NO
'wp_user'@'localhost'
def
wordpress_db
DELETE
NO
'wp_user'@'localhost'
def
wordpress_db
CREATE
NO
'wp_user'@'localhost'
def
wordpress_db
DROP
NO
'wp_user'@'localhost'
def
wordpress_db
REFERENCES
NO
'wp_user'@'localhost'
def
wordpress_db
INDEX
NO
'wp_user'@'localhost'
def
wordpress_db
ALTER
NO
'wp_user'@'localhost'
def
wordpress_db
CREATE TEMPORARY TABLES
NO
'wp_user'@'localhost'
def
wordpress_db
LOCK TABLES
NO
'wp_user'@'localhost'
def
wordpress_db
EXECUTE
NO
'wp_user'@'localhost'
def
wordpress_db
CREATE VIEW
NO
'wp_user'@'localhost'
def
wordpress_db
SHOW VIEW
NO
'wp_user'@'localhost'
def
wordpress_db
CREATE ROUTINE
NO
'wp_user'@'localhost'
def
wordpress_db
ALTER ROUTINE
NO
'wp_user'@'localhost'
def
wordpress_db
EVENT
NO
'wp_user'@'localhost'
def
wordpress_db
TRIGGER
NO

What could be the problem? It seems to me WordPress is trying to access the table wordpress_db.wp_options before creating it.

Update: if I create the database tables manually on the Google Cloud SQL instance, and then go to http://www.mydomain.com/wordpress/ I get the message:

wordpress error establishing a database connection