Start with quick checks: confirm your site address, database name, user, and...

https://echo-wiki.win/index.php/How_Long_Does_It_Take_for_MySQL_to_Come_Back_After_a_Crash%3F

Start with quick checks: confirm your site address, database name, user, and password, then check whether your host is down. If details look right, review wp-config.php, database access, and server logs