I have changed the searchindex table on my MediaWiki-based site to InnoDB. I have not done any formal tests, but the problems I noticed with searches against the MyISAM-based table were solved. I have noted two things that may be useful for others to know if they make the same change: rebuildtextindex.php deletes two search indexes for the table and then tries to create them again in one go. With some versions of MySQL (certainly 5.7.22) this crashes the script, for only one InnoDB fulltext index can be made at a time. Another problem is that searches that include a hyphen followed by a space or a hyphen ending the search string cause a "Wikimedia\Rdbms\DBQueryError". (On MediaWiki 1.30).