Why does a simple query in mysql periodically slow down?

Question

MySQL

Periodically slows down a simple request. Why?
Log of similar requests over time:

11:50:21 - query time: 0.62003. pid:5028534
12:09:08 - query time:0.03472. pid:5028717
12:10:54 - query time:0.43697. pid:5028717
12:17:27 - query time:157.7397. pid:5028717
12:17:27 - query time:0.02519. pid:5028717
12:17:28 - query time:0.02408. pid:5028717
12:28:13 - query time:0.22632. pid:5028534
12:42:13 - query time:0.3948. pid:5028717

The request itself:

SELECT UNIX_TIMESTAMP(NOW()) - UNIX_TIMESTAMP(action_history_timestamp) AS
diff_in_seconds, action_target_id 
FROM action_history WHERE action_id = 11 && user_id = '1111' && action_target_id ='1111' ORDER BY action_history_timestamp DESC LIMIT 1

The table has about 30 million records. There are indexes.

Answer 1

I think this is due to ORDER BY and LIMIT, because for these instructions to work, the result of the query is placed in a temporary table in memory. That is, I think you can increase some parameters in my.cnf - sort_buffer_size.

Answer 2

Perhaps other requests/processes on the server?