mediawiki stops working after an update

Problem

mediawiki stops working after an update (on gentoo)

Errors

Browser errors when trying to load the Mediawiki Main page of a wiki

Database error
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A database query syntax error has occurred. This may indicate a bug in the software. The last attempted database query was: 

(SQL query hidden)

from within function "Revision::fetchFromConds". Database returned error "1054: Unknown column 'rev_sha1' in 'field list' (localhost)".

Solution

change to the maintenance sub-directory (it is inide the mediawiki root directory) and execute the update script:

$ php update.php
MediaWiki 1.20.6 Updater


Going to run database updates for mediawiki
Depending on the size of your database this may take a while!
Abort with control-c in the next five seconds (skip this countdown with --quick) ... 0
...have ipb_id field in ipblocks table.
...have ipb_expiry field in ipblocks table.
...already have interwiki table
...OUTPUT TRUNCATED
Populating img_sha1 field
Done 0 files in 0.0 seconds
Fixing protocol-relative entries in the externallinks table...
Done, 0 rows updated.

Done.

When completed, I could again load my wiki main page.