I don't think a call for optimisation is called for here, especially considering the fact that a lot of optimisation has already been done on this report.

Besides, there are ways to greatly speed up the display of the grader report, for example by hiding the user pics. For example, with my test data of 15 grade items and 1000 students on 1 page, it took 400s to load the page with user pics, but only 23s to load it without the user pics...

But if you have a strategy in mind for optimising, please share it! In the meantime I will close this issue.

When entering the gradebook for any of his courses, the entire Moodle instance grinds to a halt and the MYSQL server pegs at 100% CPU usage.

Any ideas?

Petr, can you update us with the current status on those initial calculations and if they are unavoidable then can we put in a message so the user knows what is happening at least?

see the linked bugs for details, thanks for the report

SELECT DISTINCT go.userid
FROM mdl_19_grade_grades go
JOIN mdl_19_grade_items gi ON gi.id = go.itemid
LEFT OUTER JOIN mdl_19_grade_grades g
ON ( g.userid = go.userid AND g.itemid =1799 )
WHERE gi.id <>1799 AND g.id IS NULL ;

Five seconds for one user id item is way too expensive! If we can optimize this query then I think we would see lots of improvement.

The above query has an unnecessary table join to grade_items gi. I run and equivilent query removing the unnecessary grade_items join and replaced the gi.id <> 1799 with go.itemid <> 1799. The equivilent query is consistently 0.34 second instead of 5 sectonds. If we can replace this in the code as a patch I think will help.

SELECT DISTINCT go.userid
FROM mdl_19_grade_grades go
LEFT OUTER JOIN mdl_19_grade_grades g
ON ( g.userid = go.userid AND g.itemid =1799 )
WHERE go.itemid <>1799 AND g.id IS NULL;