Yongho Kim wrote: [snip]
If this is the case, why is given language MediaWiki X (let's say the english installation) not provided with the MySQL user and password for the UploadDBname "commonswiki"?
It's accessed on the same database connection, so your DB user needs permissions on the shared database as well.
For instance, our MediaWiki installs at mpkb.net are structured as follows:
MySQL english wiki (/en) DB mpkbnet_wiki, prefix en_ (en_archive, en_brokenlinks, etc..) spanish wiki (/es) DB mpkbnet_wiki, prefix es_ (es_archive, es_brokenlinks) user for mpkbnet_wiki = mpkbnet_mpkbnet
If you're using prefixes, you may also need to set $wgSharedUploadDBprefix. (You did look in DefaultSettings.php for all the available settings, right?) I've never tested it with prefixes, so can't guarantee it'll work properly.
But still, I can't see how one wiki would be able to access DB information for the other "commons" wiki.
You can access as many databases on the server as you like, as long as the user has permissions for them.
-- brion vibber (brion @ pobox.com)