TODO

These notes concern Bug #167.
The file should be removed before merging into master.

I.  Slow grading.

Hopefully this is improved by the new index timereviewed

II.  Slow matchmaking

Dubious code.
A.  file classes/matchmaking/n_closest/n_closest_selector.php, line 88-90.
The SQL query orders by the absolute value of a difference comparing the rating with a certain target value. A suitable index may or may not help here.
Three columns are involved, and you probably want to order before the the inequality constraints. I am not sure if postgres would do that efficiently. Two possible alternatives
1 remove the blacklisted question at the client.
2 create new tables where the blacklist can be filtered out in one constraint. This may or may not be feasible.

B. inactive_attempts() in classes/capquiz_question_attempt.php
This is the function to make the blacklist, to avoid frequent repeat questions.
This appears to retrieve every attempt from the DB, with no obvious reason. The SQL query should be critically reviewed.

The blacklist handling should probably be simplified, one way or another.  Suggestions:
a. It may be better to store the blacklist in a field for each capquiz user, rather than recreating it from the attempts.
b. It may be better to filter out the forbidden questions in the client, rather than having a long list of inequality constraints in an SQL call.