[#MDL-22098] Broken caching in the grade item classes leads ot O(n) DB queries in the grader report - Moodle Tracker

Details

Type: Bug
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: 1.9.8
Fix Version/s: 1.9.9
Component/s: Gradebook
Labels:
None

Affected Branches:
MOODLE_19_STABLE
Fixed Branches:
MOODLE_19_STABLE

Description

I think the diff makes the problem clear.

Index: lib/grade/grade_item.php
@@ -871,7 +871,7 @@
      * @return object Grade_category
      */
     function load_item_category() {
-        if (empty($this->category->id)) {
+        if (empty($this->item_category->id)) {
             $this->item_category = $this->get_item_category();
         }
         return $this->item_category;

This was causing one DB query per category, per student, when showing the grader report, which is very, very bad.

Andy, adding you as QA assignee, because I believe you are Mr Gradebook these days.

Issue Links

This issue has been marked as being related by:
MDL-22110	Check the gradebook for additional O(n) queries

Activity

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Tim Hunt added a comment - 16/Apr/10 12:41 AM

This issue has been fixed.

However, there seems to be plenty more unnecessarily inefficient database usage in the gradebook.

Andy, if you have time, can I suggest you do something to log every database query. For example just added

echo "\n<pre>", htmlspecialchars($sql), "\n";
debug_print_backtrace();
echo "</pre>"; // DONOTCOMMIT

at the top of Execute in lib/adodb/adodb.inc.php in 1.9. Then load various gradebook pages, and try to work out why is uses so many repeated queries (then fix it). Thanks.

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Tim Hunt added a comment - 16/Apr/10 12:41 AM This issue has been fixed. However, there seems to be plenty more unnecessarily inefficient database usage in the gradebook. Andy, if you have time, can I suggest you do something to log every database query. For example just added

echo "\n<pre>", htmlspecialchars($sql), "\n";
debug_print_backtrace();
echo "</pre>"; // DONOTCOMMIT

at the top of Execute in lib/adodb/adodb.inc.php in 1.9. Then load various gradebook pages, and try to work out why is uses so many repeated queries (then fix it). Thanks.

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Andrew Davis added a comment - 16/Apr/10 10:06 AM

Thanks Tim. I'll QA this and open another item to look for more performance killers once I've finished off some other tasks.

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Andrew Davis added a comment - 16/Apr/10 10:06 AM Thanks Tim. I'll QA this and open another item to look for more performance killers once I've finished off some other tasks.

People

Assignee:

Tim Hunt

Reporter:

Tim Hunt

Tester:

Nobody

Participants:

Andrew Davis, Tim Hunt

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Dates

Created:

16/Apr/10 12:35 AM

Updated:

13/Dec/10 6:39 PM

Resolved:

16/Apr/10 12:41 AM