MySQL sum query taking huge time to complete. Looking for a bottleneck

try making an index to userId like this will solve your problem:

   ALTER TABLE game_attempts ADD INDEX (userId);

mysql database performance

It suggests you are returning a large number of rows to the client.Can you add

GROUP BY userId

to make sure you return just a single row?

mysql database performance

Make an index on userId. That restricts access to records with failing userId.

CodeHunter