(string) temporary searchd error: server maxed out, retry in a second

Query: SELECT SUBSTRING_INDEX(GROUP_CONCAT(keyword), ',', 8) AS related_terms FROM search_popular WHERE (keyword LIKE 'amateur tube%' OR keyword LIKE 'amateur%' OR keyword LIKE 'tube%') AND keyword != 'amateur tube' ORDER BY hits DESC LIMIT 8
Error Message: MySQL server has gone away
Error Number: 2006