Issue: The Moodle User Log report using Standard Log is poor performing when the course has a large number of enrolled users and lots of activity.

Example of note:
mdl_logstore_standard_log size of 30372477 records

We have noticed that when a course has thousands of enrollments and course activity that generates logs record in the upwards of 40,000 records that the Moodle User Log Report (/report/log/user.php) for that couse is taking taking minutes to generate. By comparison it only takes 2 seconds to bring a comparable report up using the Legacy Logs setting.

We found the SQL in the report that causes the issue:

 SELECT * FROM mdl_logstore_standard_log WHERE courseid = '????' AND userid = '????' AND anonymous = 0 ORDER BY timecreated DESC, id DESC LIMIT 0, 100 

In testing we applied added a temporary index and it resolved the performance issue:

  create index quick_test on mdl_logstore_standard_log (courseid, userid, timecreated); 

Possibly in relation to what was done in MDL-44998