From LedHed's Wiki
Overview
Searching Wiki resulted in "a database query error has occurred". A quick peek at the logs revealed this error "/wiki/searchindex is marked as crashed and should be repaired". So how do you repair the MediaWiki search index table if MySQL doesn't know how? As it turns out its quite simple.
rebuildindex.php
Navigate to the MediaWiki root folder (probably something like /var/www/mediawiki) and run:
php maintenance/rebuildtextindex.php
Example Output
With any luck the utility will rebuild your search index and you're back in business.
> php maintenance/rebuildtextindex.php Dropping index... Rebuilding index fields for 2837 pages... 1000 Rebuild the index... Done.