Endless loop of upgrade

[Malaiac]

An endless loop of upgrade can happen.
It seems the cause is the test in wp_upgrade()

	if ( $wp_db_version == $wp_current_db_version )
		return;

While the test in admin.php is :

if ( get_option('db_version') != $wp_db_version ) {
	wp_redirect(admin_url('upgrade.php?_wp_http_referer=' . urlencode(stripslashes($_SERVER['REQUEST_URI']))));
	exit;
}

I just got a WP2.7 install with

// in upgrade.php
echo "<br />$wp_db_version == $wp_current_db_version";
// > 9872 == 9872

so the upgrade process never take place
but

// in admin.php
echo get_option('db_version') .' != '.$wp_db_version;
// > 9771 != 9872

always redirect

That looks like you are using some form of object cache and the options cache has old data in it.

the Upgrade/Install process uses it's own version of get_option which goes straight to the db every time without going near a cache.

As far as the database is concerned you have upgraded.

But your cache doesn't think so.

The call to update_option at the end of the upgrade seems to have made it to the db but not into the cache you are using.

I have enable_cache on, so it may be that
the test in upgrade.php should have a update_option on wp version

If you're using the Memcache object cache backend, upgrade to the latest version, which has a fix for this. I'm closing as wontfix, because it's a bug in a backend, not WP, that is causing the discrepancy.